feat(session): add turn diff route

GET /api/session/:sessionID/diff?messageID&to&context returns FileDiff.Info[] for the turn containing a user message (default: the newest one), or the contiguous range through a later user message's turn. A turn runs from the first prompt after the Session was last idle until its idle marker, so steers belong to the turn they interrupted; Sessions without markers fall back to prompt-to-next-prompt. The diff compares the range's first recorded step snapshot with its last recorded one, or with the working copy only while the Session is actively executing, resolves the snapshot repository from the Location in effect at the range (rejecting ranges that span a move), and defaults to full-file patches like vcs.diff. Shared missingMessage and failedSnapshot handler helpers replace the inlined mappings in the session handlers.

packages/client/src/effect/api/api.ts

@@ -17,6 +17,7 @@ import type { PromptInput } from "@opencode-ai/schema/prompt-input"
 import type { AgentAttachment } from "@opencode-ai/schema/prompt"
 import type { Skill } from "@opencode-ai/schema/skill"
 import type { Event } from "@opencode-ai/schema/event"
+import type { FileDiff } from "@opencode-ai/schema/file-diff"
 import type { InstructionEntry } from "@opencode-ai/schema/instruction-entry"
 import type { Schema } from "effect"
 import type { EventLog } from "@opencode-ai/schema/event-log"
@@ -36,7 +37,6 @@ import type { PtyTicket } from "@opencode-ai/schema/pty-ticket"
 import type { Reference } from "@opencode-ai/schema/reference"
 import type { Worktree } from "@opencode-ai/schema/worktree"
 import type { Vcs } from "@opencode-ai/schema/vcs"
-import type { FileDiff } from "@opencode-ai/schema/file-diff"
 import type { WebSearch } from "@opencode-ai/schema/websearch"
 import type { Config } from "@opencode-ai/schema/config"
 
@@ -360,6 +360,15 @@ export type SessionContextInput = { readonly sessionID: Session.ID }
 export type SessionContextOutput = ReadonlyArray<SessionMessage.Info>
 export type SessionContextOperation<E = never> = (input: SessionContextInput) => Effect.Effect<SessionContextOutput, E>
 
+export type SessionDiffInput = {
+  readonly sessionID: Session.ID
+  readonly messageID?: SessionMessage.ID | undefined
+  readonly to?: SessionMessage.ID | undefined
+  readonly context?: number | undefined
+}
+export type SessionDiffOutput = ReadonlyArray<FileDiff.Info>
+export type SessionDiffOperation<E = never> = (input: SessionDiffInput) => Effect.Effect<SessionDiffOutput, E>
+
 export type SessionInboxListInput = { readonly sessionID: Session.ID }
 export type SessionInboxListOutput = ReadonlyArray<SessionInbox.Info>
 export type SessionInboxListOperation<E = never> = (
@@ -1133,6 +1142,7 @@ export interface SessionApi<E = never> {
     readonly commit: SessionRevertCommitOperation<E>
   }
   readonly context: SessionContextOperation<E>
+  readonly diff: SessionDiffOperation<E>
   readonly inbox: {
     readonly list: SessionInboxListOperation<E>
     readonly cancel: SessionInboxCancelOperation<E>

packages/client/src/effect/generated/client.ts

@@ -68,6 +68,8 @@ import type {
   SessionRevertCommitOutput,
   SessionContextInput,
   SessionContextOutput,
+  SessionDiffInput,
+  SessionDiffOutput,
   SessionInboxListInput,
   SessionInboxListOutput,
   SessionInboxCancelInput,
@@ -594,6 +596,17 @@ const EndpointSessionContext = (raw: RawClient["server.session"]) => (input: Ses
     ),
   )
 
+const EndpointSessionDiff = (raw: RawClient["server.session"]) => (input: SessionDiffInput) =>
+  preserveEffect<SessionDiffOutput>()(
+    raw["session.diff"]({
+      params: { sessionID: input["sessionID"] },
+      query: { messageID: input["messageID"], to: input["to"], context: input["context"] },
+    }).pipe(
+      Effect.mapError(mapClientError),
+      Effect.map((value) => value.data),
+    ),
+  )
+
 const EndpointSessionInboxList = (raw: RawClient["server.session"]) => (input: SessionInboxListInput) =>
   preserveEffect<SessionInboxListOutput>()(
     raw["session.inbox.list"]({ params: { sessionID: input["sessionID"] } }).pipe(
@@ -744,6 +757,7 @@ const adaptGroupSession = (raw: RawClient["server.session"]) => ({
     commit: EndpointSessionRevertCommit(raw),
   },
   context: EndpointSessionContext(raw),
+  diff: EndpointSessionDiff(raw),
   inbox: {
     list: EndpointSessionInboxList(raw),
     cancel: EndpointSessionInboxCancel(raw),

packages/client/src/promise/generated/client.ts

@@ -62,6 +62,8 @@ import type {
   SessionRevertCommitOutput,
   SessionContextInput,
   SessionContextOutput,
+  SessionDiffInput,
+  SessionDiffOutput,
   SessionInboxListInput,
   SessionInboxListOutput,
   SessionInboxCancelInput,
@@ -844,6 +846,18 @@ export function make(options: ClientOptions) {
           },
           requestOptions,
         ).then((value) => value.data),
+      diff: (input: SessionDiffInput, requestOptions?: RequestOptions) =>
+        request<{ readonly data: SessionDiffOutput }>(
+          {
+            method: "GET",
+            path: `/api/session/${encodeURIComponent(input.sessionID)}/diff`,
+            query: { messageID: input["messageID"], to: input["to"], context: input["context"] },
+            successStatus: 200,
+            declaredStatuses: [400, 401, 404, 500],
+            empty: false,
+          },
+          requestOptions,
+        ).then((value) => value.data),
       inbox: {
         list: (input: SessionInboxListInput, requestOptions?: RequestOptions) =>
           request<{ readonly data: SessionInboxListOutput }>(

packages/client/src/promise/generated/types.ts

@@ -147,6 +147,14 @@ export type SessionProviderContextProvenance = {
   endpoint: string
 }
 
+export type SessionMessageIdle = {
+  id: string
+  metadata?: { [x: string]: JsonValue }
+  time: { created: number }
+  type: "idle"
+  outcome: "succeeded" | "failed" | "interrupted"
+}
+
 export type SessionActive = { type: "running" }
 
 export type SessionInboxDelivery = "steer" | "queue"
@@ -2177,6 +2185,7 @@ export type SessionMessageInfo =
   | SessionMessageShell
   | SessionMessageAssistant
   | SessionMessageCompaction
+  | SessionMessageIdle
 
 export type SessionMessageContentUpdated = {
   id: string
@@ -3122,6 +3131,13 @@ export type SessionImportInput = {
               readonly error: { readonly type: string; readonly message: string; readonly status?: number }
             }
         )
+      | {
+          readonly id: string
+          readonly metadata?: { readonly [x: string]: JsonValue }
+          readonly time: { readonly created: number }
+          readonly type: "idle"
+          readonly outcome: "succeeded" | "failed" | "interrupted"
+        }
     >
     readonly location?: { readonly directory: string; readonly workspaceID?: string } | null
   }["info"]
@@ -3413,6 +3429,13 @@ export type SessionImportInput = {
               readonly error: { readonly type: string; readonly message: string; readonly status?: number }
             }
         )
+      | {
+          readonly id: string
+          readonly metadata?: { readonly [x: string]: JsonValue }
+          readonly time: { readonly created: number }
+          readonly type: "idle"
+          readonly outcome: "succeeded" | "failed" | "interrupted"
+        }
     >
     readonly location?: { readonly directory: string; readonly workspaceID?: string } | null
   }["messages"]
@@ -3704,6 +3727,13 @@ export type SessionImportInput = {
               readonly error: { readonly type: string; readonly message: string; readonly status?: number }
             }
         )
+      | {
+          readonly id: string
+          readonly metadata?: { readonly [x: string]: JsonValue }
+          readonly time: { readonly created: number }
+          readonly type: "idle"
+          readonly outcome: "succeeded" | "failed" | "interrupted"
+        }
     >
     readonly location?: { readonly directory: string; readonly workspaceID?: string } | null
   }["location"]
@@ -4193,6 +4223,27 @@ export type SessionContextInput = { readonly sessionID: { readonly sessionID: st
 
 export type SessionContextOutput = { data: Array<SessionMessageInfo> }["data"]
 
+export type SessionDiffInput = {
+  readonly sessionID: { readonly sessionID: string }["sessionID"]
+  readonly messageID?: {
+    readonly messageID?: string | undefined
+    readonly to?: string | undefined
+    readonly context?: number | undefined
+  }["messageID"]
+  readonly to?: {
+    readonly messageID?: string | undefined
+    readonly to?: string | undefined
+    readonly context?: number | undefined
+  }["to"]
+  readonly context?: {
+    readonly messageID?: string | undefined
+    readonly to?: string | undefined
+    readonly context?: number | undefined
+  }["context"]
+}
+
+export type SessionDiffOutput = { data: Array<FileDiffInfo> }["data"]
+
 export type SessionInboxListInput = { readonly sessionID: { readonly sessionID: string }["sessionID"] }
 
 export type SessionInboxListOutput = { data: Array<SessionInboxInfo> }["data"]

packages/core/src/git.ts

@@ -9,6 +9,7 @@ import { AppProcess } from "@opencode-ai/util/process"
 import { makeGlobalNode } from "@opencode-ai/util/effect/app-node"
 import { File } from "./file.js"
 import { KeyedMutex } from "./effect/keyed-mutex.js"
+import { VcsPatch } from "./vcs/patch.js"
 
 export class Repository extends Schema.Class<Repository>("Git.Repository")({
   worktree: AbsolutePath,
@@ -308,7 +309,7 @@ const layer = Layer.effect(
       operationName: OperationError["operation"],
       repository: Repository,
       args: string[],
-      options?: { stdin?: string; env?: Record<string, string> },
+      options?: { stdin?: string; env?: Record<string, string>; maxOutputBytes?: number },
     ) {
       const result = yield* proc
         .run(
@@ -317,7 +318,7 @@ const layer = Layer.effect(
             env: options?.env,
             extendEnv: true,
           }),
-          { stdin: options?.stdin },
+          { stdin: options?.stdin, maxOutputBytes: options?.maxOutputBytes },
         )
         .pipe(
           Effect.mapError(
@@ -331,7 +332,8 @@ const layer = Layer.effect(
           ),
         )
       const text = result.stdout.toString("utf8")
-      if (result.exitCode === 0) return { text, stderr: result.stderr.toString("utf8") }
+      if (result.exitCode === 0)
+        return { text, stderr: result.stderr.toString("utf8"), truncated: result.stdoutTruncated }
       return yield* new OperationError({
         operation: operationName,
         directory: repository.worktree,
@@ -385,9 +387,7 @@ const layer = Layer.effect(
       maximumUntrackedFileBytes?: number
     }) {
       const list = (args: string[]) =>
-        repositoryOperation("refresh", input.repository, args).pipe(
-          Effect.map((result) => result.text.split("\0").filter(Boolean)),
-        )
+        repositoryOperation("refresh", input.repository, args).pipe(Effect.map((result) => nuls(result.text)))
       const [tracked, untracked] = yield* Effect.all(
         [
           list(["diff-files", "--name-only", "-z", "--", input.scope]),
@@ -464,13 +464,7 @@ const layer = Layer.effect(
           directory: input.repository.worktree,
           message: result.stderr.toString("utf8").trim() || "Failed to check ignored paths",
         })
-      return new Set(
-        result.stdout
-          .toString("utf8")
-          .split("\0")
-          .filter(Boolean)
-          .map((file) => RelativePath.make(file)),
-      )
+      return new Set(nuls(result.stdout.toString("utf8")).map((file) => RelativePath.make(file)))
     })
 
     const writeTree = Effect.fn("Git.tree.write")(function* (repository: Repository) {
@@ -499,19 +493,23 @@ const layer = Layer.effect(
       to: TreeID
     }) {
       // Undo needs both paths of a rename, not only its destination.
-      return (yield* repositoryOperation("list_files", input.repository, [
-        "diff",
-        "--name-only",
-        "--no-renames",
-        "-z",
-        input.from,
-        input.to,
-      ])).text
-        .split("\0")
-        .filter(Boolean)
-        .map((file) => RelativePath.make(file))
+      return nuls(
+        (yield* repositoryOperation("list_files", input.repository, [
+          "diff",
+          "--name-only",
+          "--no-renames",
+          "-z",
+          input.from,
+          input.to,
+        ])).text,
+      ).map((file) => RelativePath.make(file))
     })
 
+    /**
+     * Three batched invocations over the tree pair instead of three per file. An
+     * explicit empty selection diffs nothing; an absent one diffs every changed path.
+     * Patch output is capped like VCS diffs: files past the cap get an empty patch.
+     */
     const treeDiff = Effect.fn("Git.tree.diff")(function* (input: {
       repository: Repository
       from: TreeID
@@ -519,49 +517,57 @@ const layer = Layer.effect(
       context?: number
       paths?: readonly RelativePath[]
     }) {
-      const paths = input.paths ?? (yield* treeFiles(input))
-      return yield* Effect.forEach(paths, (file) =>
-        Effect.gen(function* () {
-          const statusText = (yield* repositoryOperation("diff", input.repository, [
+      if (input.paths?.length === 0) return []
+      const args = ["--no-renames", input.from, input.to, "--", ...(input.paths ?? [])]
+      // Patch headers have no -z form: unquoted paths keep chunksByFile matching non-ASCII names.
+      const [names, numbers, patch] = yield* Effect.all(
+        [
+          repositoryOperation("diff", input.repository, ["diff", "--name-status", "-z", ...args]),
+          repositoryOperation("diff", input.repository, ["diff", "--numstat", "-z", ...args]),
+          repositoryOperation(
             "diff",
-            "--name-status",
-            "--no-renames",
-            input.from,
-            input.to,
-            "--",
-            file,
-          ])).text.trim()
-          const status = statusText.startsWith("A") ? "added" : statusText.startsWith("D") ? "deleted" : "modified"
-          const stats = (yield* repositoryOperation("diff", input.repository, [
-            "diff",
-            "--numstat",
-            "--no-renames",
-            input.from,
-            input.to,
-            "--",
-            file,
-          ])).text.split("\t")
-          const binary = stats[0] === "-" || stats[1] === "-"
-          const patch = binary
-            ? ""
-            : (yield* repositoryOperation("diff", input.repository, [
-                "diff",
-                `--unified=${input.context ?? 3}`,
-                "--no-renames",
-                input.from,
-                input.to,
-                "--",
-                file,
-              ])).text
-          return {
-            file,
-            status,
-            additions: binary ? 0 : Number(stats[0] ?? 0),
-            deletions: binary ? 0 : Number(stats[1] ?? 0),
-            patch,
-          } satisfies File.Diff
+            input.repository,
+            ["-c", "core.quotepath=false", "diff", "--no-ext-diff", `--unified=${input.context ?? 3}`, ...args],
+            { maxOutputBytes: VcsPatch.MAX_TOTAL_PATCH_BYTES },
+          ),
+        ],
+        { concurrency: 3 },
+      )
+      const statuses = nuls(names.text)
+      const files = statuses.flatMap((code, index) => {
+        const file = statuses[index + 1]
+        if (index % 2 !== 0 || !file) return []
+        return [
+          {
+            file: RelativePath.make(file),
+            status: code.startsWith("A") ? "added" : code.startsWith("D") ? "deleted" : "modified",
+          } as const,
+        ]
+      })
+      const stats = new Map(
+        nuls(numbers.text).flatMap((line) => {
+          const [additions, deletions, ...file] = line.split("\t")
+          if (!additions || !deletions || file.length === 0) return []
+          return [
+            [
+              file.join("\t"),
+              additions === "-" || deletions === "-"
+                ? { binary: true, additions: 0, deletions: 0 }
+                : { binary: false, additions: Number(additions), deletions: Number(deletions) },
+            ] as const,
+          ]
         }),
       )
+      const patches = VcsPatch.chunksByFile(patch, (index) => files[index]?.file)
+      return files.map((entry) => {
+        const stat = stats.get(entry.file)
+        return {
+          ...entry,
+          additions: stat?.additions ?? 0,
+          deletions: stat?.deletions ?? 0,
+          patch: stat?.binary ? "" : (patches.get(entry.file) ?? VcsPatch.emptyPatch(entry.file)),
+        } satisfies File.Diff
+      })
     })
 
     const hasEntry = Effect.fnUntraced(function* (repository: Repository, tree: TreeID, file: RelativePath) {
@@ -733,6 +739,11 @@ function execute(cwd: string, proc: AppProcess.Interface, args: string[]) {
     )
 }
 
+/** Split NUL-terminated git output into its records. */
+function nuls(text: string) {
+  return text.split("\0").filter(Boolean)
+}
+
 function resolvePath(cwd: string, value: string) {
   const trimmed = value.replace(/[\r\n]+$/, "")
   if (!trimmed) return cwd

packages/core/src/session.ts

@@ -57,8 +57,11 @@ import { SessionModelTransport } from "./session/model-transport.js"
 import { llmClient } from "./effect/app-node-platform.js"
 import { Snapshot } from "./snapshot.js"
 import { Session } from "./session/session.js"
+import { SessionDiff, TurnRangeError } from "./session/diff.js"
+import { LocationServiceMap } from "./location-service-map.js"
 import { FSUtil } from "@opencode-ai/util/fs-util"
 import type { EventLog } from "@opencode-ai/schema/event-log"
+import type { FileDiff } from "@opencode-ai/schema/file-diff"
 import { Job } from "./job.js"
 import type { Command } from "./command.js"
 import { SessionEnvironment } from "./session/environment.js"
@@ -113,6 +116,7 @@ export {
 type InboxItemRef = { readonly sessionID: SessionSchema.ID; readonly inboxID: SessionMessage.ID }
 
 export { DestinationNotFoundError, DestinationNotDirectoryError, DestinationUnavailableError }
+export { TurnRangeError }
 
 export interface Interface {
   readonly list: (input?: ListInput) => Effect.Effect<{
@@ -142,6 +146,13 @@ export interface Interface {
   readonly context: (
     sessionID: SessionSchema.ID,
   ) => Effect.Effect<SessionMessage.Info[], NotFoundError | MessageDecodeError>
+  /** Structured diffs of the files changed by a turn or range of turns; see `SessionDiff.turn`. */
+  readonly diff: (input: {
+    readonly sessionID: SessionSchema.ID
+    readonly messageID?: SessionMessage.ID
+    readonly to?: SessionMessage.ID
+    readonly context?: number
+  }) => Effect.Effect<readonly FileDiff.Info[], NotFoundError | MessageNotFoundError | TurnRangeError | Snapshot.Error>
   /**
    * Durable admitted session work not yet visible in projected history,
    * ordered by admission. Includes unpromoted user and synthetic inputs and
@@ -230,6 +241,7 @@ const layer = Layer.effect(
     const moves = yield* SessionMove.Service
     const jobs = yield* Job.Service
     const environments = yield* SessionEnvironment.Service
+    const locations = yield* LocationServiceMap.Service
     const sessions = yield* Session.make()
     const isDurableSessionEvent = Schema.is(SessionEvent.Durable)
 
@@ -362,6 +374,17 @@ const layer = Layer.effect(
         yield* result.get(sessionID)
         return yield* store.context(sessionID)
       }),
+      diff: Effect.fn("Session.diff")(function* (input) {
+        const session = yield* result.get(input.sessionID)
+        const active = yield* execution.isActive(input.sessionID)
+        return yield* SessionDiff.turn(db, locations, {
+          session,
+          active,
+          messageID: input.messageID,
+          to: input.to,
+          context: input.context,
+        })
+      }),
       inbox: (sessionID) => sessions.forSession(sessionID).inbox(),
       cancelInbox: (input) => sessions.forSession(input.sessionID).cancelInbox(input.inboxID),
       steerInbox: (input) => sessions.forSession(input.sessionID).steerInbox(input.inboxID),
@@ -450,6 +473,7 @@ export const node: LayerNode.Provider<Service, never, typeof Node.tags.values.gl
     SessionInbox.node,
     SessionMove.node,
     SessionProjector.node,
+    LocationServiceMap.node,
     FSUtil.node,
     App.node,
   ],

packages/core/src/session/diff.ts

@@ -0,0 +1,138 @@
+export * as SessionDiff from "./diff.js"
+
+import { and, asc, eq, gt, inArray, lt, or, sql } from "drizzle-orm"
+import { Context, Effect, Schema } from "effect"
+import { Location } from "@opencode-ai/schema/location"
+import { Database } from "../database/database.js"
+import { LocationServiceMap } from "../location-service-map.js"
+import { Snapshot } from "../snapshot.js"
+import { PATCH_CONTEXT_LINES } from "../vcs/patch.js"
+import { MessageNotFoundError } from "./error.js"
+import { SessionMessage } from "./message.js"
+import { SessionSchema } from "./schema.js"
+import { SessionMessageTable } from "./sql.js"
+
+export class TurnRangeError extends Schema.TaggedError<TurnRangeError>()("Session.TurnRangeError", {
+  sessionID: SessionSchema.ID,
+  field: Schema.Literals(["messageID", "to"]),
+  message: Schema.String,
+}) {}
+
+const decodeLocation = Schema.decodeUnknownSync(Schema.fromJsonString(Location.Ref))
+
+/**
+ * Diff the files changed by the turn containing a user message. A turn runs from
+ * the first prompt after the Session was last idle until the next idle marker, so
+ * prompts steered in while it was busy belong to the same turn; `to` extends the
+ * range through the turn containing a later user message. Compares the range's
+ * first recorded start snapshot with its last recorded end snapshot; only a step
+ * still running in the active Session compares against the working copy. Like VCS
+ * diffs, an omitted `context` yields full-file patches.
+ *
+ * A Session without any idle marker predates them, so its prompts span until the
+ * next user message instead.
+ *
+ * Snapshot trees live in the repository of the Location that captured them, so a
+ * range spanning a location switch is rejected rather than diffed wrongly.
+ */
+export const turn = Effect.fn("SessionDiff.turn")(function* (
+  db: Database.Interface["db"],
+  locations: Context.Service.Shape<typeof LocationServiceMap.Service>,
+  input: {
+    readonly session: SessionSchema.Info
+    /** The process is currently executing this Session. */
+    readonly active: boolean
+    readonly messageID?: SessionMessage.ID
+    readonly to?: SessionMessage.ID
+    readonly context?: number
+  },
+) {
+  const sessionID = input.session.id
+  const rows = yield* db
+    .select({ id: SessionMessageTable.id, type: SessionMessageTable.type, seq: SessionMessageTable.seq })
+    .from(SessionMessageTable)
+    .where(
+      and(
+        eq(SessionMessageTable.session_id, sessionID),
+        or(
+          inArray(SessionMessageTable.type, ["user", "idle"]),
+          input.messageID ? eq(SessionMessageTable.id, input.messageID) : undefined,
+          input.to ? eq(SessionMessageTable.id, input.to) : undefined,
+        ),
+      ),
+    )
+    .orderBy(asc(SessionMessageTable.seq))
+    .all()
+    .pipe(Effect.orDie)
+  const users = rows.filter((row) => row.type === "user")
+  const markers = rows.filter((row) => row.type === "idle")
+  const resolve = Effect.fn(function* (field: "messageID" | "to", id: SessionMessage.ID) {
+    const row = rows.find((row) => row.id === id)
+    if (!row) return yield* new MessageNotFoundError({ sessionID, messageID: id })
+    if (row.type !== "user")
+      return yield* new TurnRangeError({ sessionID, field, message: `Message ${id} is not a user message` })
+    return row
+  })
+  const anchor = input.messageID ? yield* resolve("messageID", input.messageID) : users[users.length - 1]
+  if (!anchor) return []
+  const last = input.to ? yield* resolve("to", input.to) : anchor
+  if (last.seq < anchor.seq)
+    return yield* new TurnRangeError({ sessionID, field: "to", message: `Message ${last.id} precedes ${anchor.id}` })
+  // Without any marker, history predates idle markers and a prompt's turn ends at the next prompt.
+  const legacy = markers.length === 0
+  // The turn opens with the first prompt after the previous idle marker; the anchor itself is the latest candidate.
+  const opened = markers.findLast((row) => row.seq < anchor.seq)?.seq ?? -1
+  const start = legacy ? anchor.seq : (users.find((row) => row.seq > opened)?.seq ?? anchor.seq)
+  const end = legacy ? users.find((row) => row.seq > last.seq)?.seq : markers.find((row) => row.seq > last.seq)?.seq
+  const steps = yield* db
+    .select({
+      seq: SessionMessageTable.seq,
+      start: sql<string | null>`json_extract(${SessionMessageTable.data}, '$.snapshot.start')`,
+      end: sql<string | null>`json_extract(${SessionMessageTable.data}, '$.snapshot.end')`,
+      completed: sql<number | null>`json_extract(${SessionMessageTable.data}, '$.time.completed')`,
+    })
+    .from(SessionMessageTable)
+    .where(
+      and(
+        eq(SessionMessageTable.session_id, sessionID),
+        eq(SessionMessageTable.type, "assistant"),
+        gt(SessionMessageTable.seq, start),
+        end === undefined ? undefined : lt(SessionMessageTable.seq, end),
+      ),
+    )
+    .orderBy(asc(SessionMessageTable.seq))
+    .all()
+    .pipe(Effect.orDie)
+  const first = steps[0]
+  const final = steps[steps.length - 1]
+  const from = steps.find((step) => step.start)?.start
+  if (!first || !final || !from) return []
+  const switches = yield* db
+    .select({
+      seq: SessionMessageTable.seq,
+      location: sql<string>`json_extract(${SessionMessageTable.data}, '$.location')`,
+      previous: sql<string | null>`json_extract(${SessionMessageTable.data}, '$.previous.location')`,
+    })
+    .from(SessionMessageTable)
+    .where(and(eq(SessionMessageTable.session_id, sessionID), eq(SessionMessageTable.type, "location-switched")))
+    .orderBy(asc(SessionMessageTable.seq))
+    .all()
+    .pipe(Effect.orDie)
+  if (switches.some((row) => row.seq > first.seq && row.seq < final.seq))
+    return yield* new TurnRangeError({ sessionID, field: "to", message: "Turn range spans a location change" })
+  const before = switches.findLast((row) => row.seq < first.seq)?.location
+  const after = switches.find((row) => row.seq > first.seq)?.previous
+  const location = before ? decodeLocation(before) : after ? decodeLocation(after) : input.session.location
+  const recorded = steps.findLast((step) => step.end)?.end
+  return yield* Effect.gen(function* () {
+    const snapshot = yield* Snapshot.Service
+    const running = input.active && final.completed === null
+    const to = running ? ((yield* snapshot.capture()) ?? recorded) : recorded
+    if (!to) return []
+    return yield* snapshot.diff({
+      from: Snapshot.ID.make(from),
+      to: Snapshot.ID.make(to),
+      context: input.context ?? PATCH_CONTEXT_LINES,
+    })
+  }).pipe(Effect.provide(locations.get(location)))
+})

packages/core/src/session/message-updater.ts

@@ -60,6 +60,21 @@ export function update(adapter: Adapter, event: SessionEvent.DurableEvent) {
     )
   })
 
+  const idle = (outcome: SessionMessage.Idle["outcome"]) =>
+    clearCurrentRetry.pipe(
+      Effect.andThen(
+        adapter.appendMessage(
+          SessionMessage.Idle.make({
+            id: SessionMessage.ID.fromEvent(event.id),
+            type: "idle",
+            outcome,
+            metadata: event.metadata,
+            time: { created },
+          }),
+        ),
+      ),
+    )
+
   const project = pipe(
     Match.type<SessionEvent.DurableEvent>(),
     Match.discriminatorsExhaustive("type")({
@@ -123,9 +138,11 @@ export function update(adapter: Adapter, event: SessionEvent.DurableEvent) {
       "session.inbox.cancelled": () => Effect.void,
       "session.inbox.delivery.changed": () => Effect.void,
       "session.execution.started": () => Effect.void,
-      "session.execution.succeeded": () => clearCurrentRetry,
-      "session.execution.failed": () => clearCurrentRetry,
-      "session.execution.interrupted": () => clearCurrentRetry,
+      "session.execution.succeeded": () => idle("succeeded"),
+      "session.execution.failed": () => idle("failed"),
+      // Shutdown keeps the execution claim and the resumed drain continues the turn.
+      "session.execution.interrupted": (event) =>
+        event.data.reason === "shutdown" ? clearCurrentRetry : idle("interrupted"),
       "session.instructions.updated": (event) => {
         if (event.data.text === undefined) return Effect.void
         return adapter.appendMessage(

packages/core/src/session/runner/to-llm-message.ts

@@ -226,6 +226,7 @@ function toLLMMessage(message: SessionMessage.Info, model: Model.Ref, providerMe
   switch (message.type) {
     case "agent-switched":
     case "model-switched":
+    case "idle":
       return []
     case "location-switched":
       return [

packages/core/src/snapshot.ts

@@ -131,38 +131,55 @@ const layer = Layer.effect(
       )
     })
 
-    const compare = Effect.fnUntraced(function* (operation: "files" | "diff", input: CompareInput) {
+    const comparison = Effect.fnUntraced(function* (operation: "files" | "diff", input: CompareInput) {
       const repo = yield* repository.pipe(Effect.mapError((cause) => failure(operation, cause)))
-      const comparison = {
+      return {
+        source: repo.source,
         repository: repo.snapshotRepository,
         from: Git.TreeID.make(input.from),
         to: Git.TreeID.make(input.to),
       }
-      const files = yield* git.tree.files(comparison).pipe(Effect.mapError((cause) => failure(operation, cause)))
-      const ignored = yield* git.index
-        .ignored({ repository: repo.source, paths: files })
+    })
+
+    // Snapshots track every scoped file; the source repository's ignore rules decide what callers see.
+    const ignored = Effect.fnUntraced(function* (
+      operation: "files" | "diff",
+      source: Git.Repository,
+      paths: readonly RelativePath[],
+    ) {
+      return yield* git.index
+        .ignored({ repository: source, paths })
         .pipe(Effect.mapError((cause) => failure(operation, cause)))
-      return {
-        input: comparison,
-        files,
-        ignored,
-      }
     })
 
     const files = Effect.fn("Snapshot.files")(function* (input: CompareInput) {
-      const comparison = yield* compare("files", input)
-      return comparison.files.filter((file) => !comparison.ignored.has(file))
+      const compared = yield* comparison("files", input)
+      const changed = yield* git.tree
+        .files({ repository: compared.repository, from: compared.from, to: compared.to })
+        .pipe(Effect.mapError((cause) => failure("files", cause)))
+      const skipped = yield* ignored("files", compared.source, changed)
+      return changed.filter((file) => !skipped.has(file))
     })
 
     const diff = Effect.fn("Snapshot.diff")(function* (input: DiffInput) {
-      const comparison = yield* compare("diff", input)
-      return yield* git.tree
+      if (input.paths?.length === 0) return []
+      const compared = yield* comparison("diff", input)
+      // Only an explicit selection becomes a pathspec; ignored paths are dropped from the result instead.
+      const diffs = yield* git.tree
         .diff({
-          ...comparison.input,
+          repository: compared.repository,
+          from: compared.from,
+          to: compared.to,
           context: input.context,
-          paths: (input.paths ?? comparison.files).filter((file) => !comparison.ignored.has(file)),
+          paths: input.paths,
         })
         .pipe(Effect.mapError((cause) => failure("diff", cause)))
+      const skipped = yield* ignored(
+        "diff",
+        compared.source,
+        diffs.map((file) => RelativePath.make(file.file)),
+      )
+      return diffs.filter((file) => !skipped.has(RelativePath.make(file.file)))
     })
 
     const plan = Effect.fnUntraced(function* (worktree: AbsolutePath, input: RestoreInput) {

packages/core/src/v1/config/permission.ts

@@ -25,7 +25,7 @@ const InputObject = Schema.StructWithRest(
     task: Schema.optional(Rule),
     external_directory: Schema.optional(Rule),
     question: Schema.optional(Action),
-    webfetch: Schema.optional(Action),
+    webfetch: Schema.optional(Rule),
     websearch: Schema.optional(Action),
     lsp: Schema.optional(Rule),
     doom_loop: Schema.optional(Action),

packages/core/test/config/config.test.ts

@@ -1342,6 +1342,7 @@ describe("Config", () => {
                   bash: "ask",
                   edit: { "*.md": "allow", "*": "deny" },
                   question: "deny",
+                  webfetch: { "*": "ask", "https://en.wikipedia.org/*": "allow" },
                 },
                 agent: {
                   reviewer: {
@@ -1420,6 +1421,8 @@ describe("Config", () => {
               { action: "edit", resource: "*.md", effect: "allow" },
               { action: "edit", resource: "*", effect: "deny" },
               { action: "question", resource: "*", effect: "deny" },
+              { action: "webfetch", resource: "*", effect: "ask" },
+              { action: "webfetch", resource: "https://en.wikipedia.org/*", effect: "allow" },
             ])
             expect(documents[0]?.info.agents?.reviewer).toMatchObject({
               system: "Review changes.",

packages/core/test/git.test.ts

@@ -6,6 +6,7 @@ import { Effect } from "effect"
 import { LayerNode } from "@opencode-ai/util/effect/layer-node"
 import { Git } from "@opencode-ai/core/git"
 import { AbsolutePath, RelativePath } from "@opencode-ai/core/schema"
+import { VcsPatch } from "@opencode-ai/core/vcs/patch"
 import { branch, commit, initRepo, read, withRemote } from "./fixture/git"
 import { tmpdir } from "./fixture/tmpdir"
 import { testEffect } from "./lib/effect"
@@ -196,6 +197,42 @@ describe("Git trees", () => {
     }),
   )
 
+  it.live("caps batched tree patches, keeps per-file stats past the cap, and matches non-ASCII names", () =>
+    Effect.gen(function* () {
+      const root = yield* Effect.acquireRelease(
+        Effect.promise(() => tmpdir()),
+        (dir) => Effect.promise(() => dir[Symbol.asyncDispose]()),
+      )
+      yield* Effect.promise(() => initRepo(root.path))
+      const git = yield* Git.Service
+      const repository = yield* git.repo.discover(AbsolutePath.make(root.path))
+      if (!repository) throw new Error("Repository not found")
+      const before = yield* git.tree.capture({ repository, scopes: [RelativePath.make(".")] })
+      const lines = Math.ceil(VcsPatch.MAX_TOTAL_PATCH_BYTES / 80) + 1
+      yield* Effect.promise(async () => {
+        await Bun.write(path.join(root.path, "a-small.txt"), "small\n")
+        await Bun.write(path.join(root.path, "b-large.txt"), `${"x".repeat(79)}\n`.repeat(lines))
+        await Bun.write(path.join(root.path, "c-binary.bin"), new Uint8Array([0, 1, 2, 3]))
+        await Bun.write(path.join(root.path, "a-caf\u00e9.txt"), "caf\u00e9\n")
+      })
+      const after = yield* git.tree.capture({ repository, scopes: [RelativePath.make(".")] })
+
+      const diffs = yield* git.tree.diff({ repository, from: before, to: after, context: 0 })
+      expect(diffs.map((item) => [item.file, item.status, item.additions, item.deletions])).toEqual([
+        ["a-caf\u00e9.txt", "added", 1, 0],
+        ["a-small.txt", "added", 1, 0],
+        ["b-large.txt", "added", lines, 0],
+        ["c-binary.bin", "added", 0, 0],
+      ])
+      // Patch headers are not NUL-delimited; a quoted (octal-escaped) header would orphan this chunk.
+      expect(diffs[0]?.patch).toContain("+caf\u00e9\n")
+      expect(diffs[1]?.patch).toContain("+small\n")
+      expect(diffs[2]?.patch).toBe(VcsPatch.emptyPatch("b-large.txt"))
+      expect(diffs[3]?.patch).toBe("")
+      expect(yield* git.tree.diff({ repository, from: before, to: after, paths: [] })).toEqual([])
+    }),
+  )
+
   it.live("captures, compares, previews, and restores scoped trees", () =>
     Effect.gen(function* () {
       const root = yield* Effect.acquireRelease(

packages/core/test/session-diff.test.ts

@@ -0,0 +1,198 @@
+import { $ } from "bun"
+import { describe, expect } from "bun:test"
+import fs from "fs/promises"
+import path from "path"
+import { Effect } from "effect"
+import { Agent } from "@opencode-ai/core/agent"
+import { Bus } from "@opencode-ai/core/bus"
+import { Database } from "@opencode-ai/core/database/database"
+import { AppNodeBuilder } from "@opencode-ai/core/effect/app-node-builder"
+import { LocationServiceMap } from "@opencode-ai/core/location-service-map"
+import { Model } from "@opencode-ai/core/model"
+import { Plugin } from "@opencode-ai/core/plugin"
+import { Provider } from "@opencode-ai/core/provider"
+import { AbsolutePath } from "@opencode-ai/core/schema"
+import { Session } from "@opencode-ai/core/session"
+import { SessionDiff } from "@opencode-ai/core/session/diff"
+import { SessionEvent } from "@opencode-ai/core/session/event"
+import { SessionExecution } from "@opencode-ai/core/session/execution"
+import { SessionInbox } from "@opencode-ai/core/session/inbox"
+import { SessionMessage } from "@opencode-ai/core/session/message"
+import { SessionProjector } from "@opencode-ai/core/session/projector"
+import { Snapshot } from "@opencode-ai/core/snapshot"
+import { Money } from "@opencode-ai/schema/money"
+import { LayerNode } from "@opencode-ai/util/effect/layer-node"
+import { Global } from "@opencode-ai/util/global"
+import { tempGlobalLayer } from "./fixture/global"
+import { offlineModels } from "./fixture/models"
+import { tmpdirScoped } from "./fixture/tmpdir"
+import { testEffect } from "./lib/effect"
+
+const it = testEffect(
+  AppNodeBuilder.build(
+    LayerNode.group([Database.node, Bus.node, SessionProjector.node, Session.node, LocationServiceMap.node]),
+    [Global.node.replace(tempGlobalLayer), SessionExecution.node.replace(SessionExecution.noopLayer), offlineModels],
+  ),
+)
+
+const summarize = (file: { file: string; status: string; additions: number; deletions: number }) => [
+  file.file,
+  file.status,
+  file.additions,
+  file.deletions,
+]
+
+describe("Session.diff", () => {
+  it.live(
+    "diffs the busy period containing a user message and ranges across later turns",
+    () =>
+      Effect.gen(function* () {
+        const tmp = yield* tmpdirScoped()
+        const directory = path.join(tmp.path, "project")
+        const write = (name: string, content: string) => () => Bun.write(path.join(directory, name), content)
+        yield* Effect.promise(async () => {
+          await fs.mkdir(directory)
+          await write("first.txt", "first\n")()
+          await write("second.txt", "second\n")()
+          await write("manual.txt", "manual\n")()
+          await $`git init -q`.cwd(directory).quiet()
+          await $`git -c core.fsmonitor=false add .`.cwd(directory).quiet()
+        })
+        const sessions = yield* Session.Service
+        const database = yield* Database.Service
+        const bus = yield* Bus.Service
+        const locations = yield* LocationServiceMap.Service
+        const created = yield* sessions.create({ location: { directory: AbsolutePath.make(directory) } })
+        const diff = (input?: { messageID?: SessionMessage.ID; to?: SessionMessage.ID }) =>
+          sessions
+            .diff({ sessionID: created.id, context: 0, ...input })
+            .pipe(Effect.map((files) => files.map(summarize)))
+        expect(yield* diff()).toEqual([])
+
+        yield* Effect.gen(function* () {
+          const plugins = yield* Plugin.Service
+          yield* plugins.awaitActivation
+          const snapshot = yield* Snapshot.Service
+          const usage = {
+            cost: Money.USD.zero,
+            tokens: { input: 0, output: 0, reasoning: 0, cache: { read: 0, write: 0 } },
+          }
+          const prompt = Effect.fn(function* (text: string) {
+            const admitted = yield* sessions.prompt({ sessionID: created.id, text, resume: false })
+            yield* SessionInbox.promote(database.db, bus, created.id, "steer")
+            return admitted.id
+          })
+          const step = Effect.fn(function* (edit: () => Promise<unknown>, end: "recorded" | "unrecorded" | "running") {
+            const before = yield* snapshot.capture()
+            if (!before) throw new Error("Start snapshot missing")
+            const assistantMessageID = SessionMessage.ID.create()
+            yield* bus.publish(SessionEvent.Step.Started, {
+              sessionID: created.id,
+              assistantMessageID,
+              agent: Agent.defaultID,
+              model: { id: Model.ID.make("test-model"), providerID: Provider.ID.make("test-provider") },
+              snapshot: before,
+            })
+            yield* Effect.promise(edit)
+            if (end === "running") return assistantMessageID
+            const after = end === "recorded" ? yield* snapshot.capture() : undefined
+            yield* bus.publish(SessionEvent.Step.Ended, {
+              sessionID: created.id,
+              assistantMessageID,
+              finish: "stop",
+              ...usage,
+              snapshot: after,
+              files: after && before ? yield* snapshot.files({ from: before, to: after }) : undefined,
+            })
+            return assistantMessageID
+          })
+
+          const idle = (outcome: "succeeded" | "failed") =>
+            outcome === "succeeded"
+              ? bus.publish(SessionEvent.Execution.Succeeded, { sessionID: created.id })
+              : bus.publish(SessionEvent.Execution.Failed, {
+                  sessionID: created.id,
+                  error: { type: "unknown", message: "failed" },
+                })
+
+          // Before any idle marker exists, a prompt's turn ends at the next prompt.
+          const first = yield* prompt("Edit the first file")
+          const firstStep = yield* step(write("first.txt", "first edited\n"), "recorded")
+          // Edits made while idle are not a turn's work, but a range spanning them still sees them.
+          yield* Effect.promise(write("manual.txt", "manual edited\n"))
+          const second = yield* prompt("Edit the second file")
+          yield* step(write("second.txt", "second edited\n"), "recorded")
+          expect(yield* diff()).toEqual([["second.txt", "modified", 1, 1]])
+          expect(yield* diff({ messageID: first })).toEqual([["first.txt", "modified", 1, 1]])
+
+          // Once markers exist, a turn spans a whole busy period, steers included; earlier history merges into the first one.
+          yield* idle("succeeded")
+          const third = yield* prompt("Add a third file")
+          yield* step(write("third.txt", "third\n"), "recorded")
+          const steer = yield* prompt("Also add a fourth file")
+          yield* step(write("fourth.txt", "fourth\n"), "recorded")
+          yield* idle("failed")
+          const busy = [
+            ["fourth.txt", "added", 1, 0],
+            ["third.txt", "added", 1, 0],
+          ]
+          expect(yield* diff()).toEqual(busy)
+          expect(yield* diff({ messageID: steer })).toEqual(busy)
+          expect(yield* diff({ messageID: second })).toEqual([
+            ["first.txt", "modified", 1, 1],
+            ["manual.txt", "modified", 1, 1],
+            ["second.txt", "modified", 1, 1],
+          ])
+          expect(yield* diff({ messageID: first, to: third })).toEqual([
+            ["first.txt", "modified", 1, 1],
+            ["fourth.txt", "added", 1, 0],
+            ["manual.txt", "modified", 1, 1],
+            ["second.txt", "modified", 1, 1],
+            ["third.txt", "added", 1, 0],
+          ])
+          const full = yield* sessions.diff({ sessionID: created.id, messageID: first })
+          expect(full[0]?.patch).toContain("-first\n+first edited\n")
+          expect(yield* diff({ messageID: steer, to: second }).pipe(Effect.flip)).toMatchObject({
+            _tag: "Session.TurnRangeError",
+            field: "to",
+          })
+          expect(yield* diff({ messageID: firstStep }).pipe(Effect.flip)).toMatchObject({
+            _tag: "Session.TurnRangeError",
+            field: "messageID",
+          })
+          expect(yield* diff({ messageID: SessionMessage.ID.create() }).pipe(Effect.flip)).toMatchObject({
+            _tag: "Session.MessageNotFoundError",
+          })
+
+          // A completed step without an end snapshot falls back to the last recorded end.
+          yield* prompt("Edit both files again")
+          yield* step(write("first.txt", "first edited twice\n"), "recorded")
+          yield* step(write("second.txt", "second edited twice\n"), "unrecorded")
+          yield* idle("succeeded")
+          expect(yield* diff()).toEqual([["first.txt", "modified", 1, 1]])
+
+          // Only a step still running in the active session compares against the working copy.
+          yield* prompt("Delete the manual file")
+          yield* step(() => fs.rm(path.join(directory, "manual.txt")), "running")
+          expect(yield* diff()).toEqual([])
+          const session = yield* sessions.get(created.id)
+          const live = yield* SessionDiff.turn(database.db, locations, { session, active: true, context: 0 })
+          expect(live.map(summarize)).toEqual([["manual.txt", "deleted", 0, 1]])
+
+          // Reverting removes later history, markers included; a fork keeps the copied turns.
+          yield* sessions.revert.stage({ sessionID: created.id, messageID: steer, files: false })
+          yield* sessions.revert.commit(created.id)
+          expect(yield* diff()).toEqual([["third.txt", "added", 1, 0]])
+          expect(yield* diff({ messageID: steer }).pipe(Effect.flip)).toMatchObject({
+            _tag: "Session.MessageNotFoundError",
+          })
+          const forked = yield* sessions.fork({ sessionID: created.id, boundary: { type: "through" } })
+          expect((yield* sessions.diff({ sessionID: forked.id, context: 0 })).map(summarize)).toEqual([
+            ["third.txt", "added", 1, 0],
+          ])
+        }).pipe(Effect.provide(LocationServiceMap.Service.get(created.location)))
+      }),
+    // Real Location/plugin startup and Git snapshots can exceed five seconds under CI load.
+    { timeout: 30_000 },
+  )
+})

packages/core/test/session-execution.test.ts

@@ -561,7 +561,9 @@ describe("SessionRestart background recovery", () => {
         expect(yield* restarted.pendingBackground).toEqual([])
         expect(yield* SessionInbox.list(database.db, sessionID)).toHaveLength(delivered ? 0 : 1)
         yield* SessionInbox.promote(database.db, bus, sessionID, "steer")
-        expect(yield* sessions.messages({ sessionID })).toMatchObject([
+        // Recovery ends a busy period, so an idle marker follows the notification.
+        const messages = (yield* sessions.messages({ sessionID })).filter((message) => message.type !== "idle")
+        expect(messages).toMatchObject([
           {
             id: background.notificationID,
             type: "synthetic",
@@ -569,7 +571,6 @@ describe("SessionRestart background recovery", () => {
             metadata: { state: "completed" },
           },
         ])
-        expect(yield* sessions.messages({ sessionID })).toHaveLength(1)
       }),
     )
   }

packages/protocol/openapi.json

@@ -1621,14 +1621,7 @@
             "content": {
               "application/json": {
                 "schema": {
-                  "anyOf": [
-                    {
-                      "$ref": "#/components/schemas/SessionNotFoundErrorEncoded"
-                    },
-                    {
-                      "$ref": "#/components/schemas/SessionNotFoundErrorEncoded"
-                    }
-                  ]
+                  "$ref": "#/components/schemas/SessionNotFoundErrorEncoded"
                 }
               }
             }
@@ -3249,6 +3242,152 @@
         "summary": "Get session context"
       }
     },
+    "/api/session/{sessionID}/diff": {
+      "get": {
+        "tags": ["session"],
+        "operationId": "v2.session.diff",
+        "parameters": [
+          {
+            "name": "sessionID",
+            "in": "path",
+            "schema": {
+              "type": "string",
+              "pattern": "^ses"
+            },
+            "required": true
+          },
+          {
+            "name": "messageID",
+            "in": "query",
+            "schema": {
+              "anyOf": [
+                {
+                  "type": "string",
+                  "pattern": "^msg_"
+                },
+                {
+                  "type": "null"
+                }
+              ],
+              "description": "User message whose turn to diff. Defaults to the turn of the newest user message."
+            },
+            "required": false
+          },
+          {
+            "name": "to",
+            "in": "query",
+            "schema": {
+              "anyOf": [
+                {
+                  "type": "string",
+                  "pattern": "^msg_"
+                },
+                {
+                  "type": "null"
+                }
+              ],
+              "description": "Later user message whose turn ends the range. Defaults to the turn of `messageID` alone."
+            },
+            "required": false
+          },
+          {
+            "name": "context",
+            "in": "query",
+            "schema": {
+              "anyOf": [
+                {
+                  "type": "string"
+                },
+                {
+                  "type": "null"
+                }
+              ],
+              "description": "Unchanged lines around each hunk. Omit for full-file patches."
+            },
+            "required": false
+          }
+        ],
+        "security": [],
+        "responses": {
+          "200": {
+            "description": "Success",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "type": "object",
+                  "properties": {
+                    "data": {
+                      "type": "array",
+                      "items": {
+                        "$ref": "#/components/schemas/FileDiff.Info"
+                      }
+                    }
+                  },
+                  "required": ["data"],
+                  "additionalProperties": false
+                }
+              }
+            }
+          },
+          "400": {
+            "description": "InvalidRequestError",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "anyOf": [
+                    {
+                      "$ref": "#/components/schemas/InvalidRequestErrorEncoded"
+                    },
+                    {
+                      "$ref": "#/components/schemas/InvalidRequestErrorEncoded"
+                    }
+                  ]
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "UnauthorizedError",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/UnauthorizedErrorEncoded"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "MessageNotFoundError | SessionNotFoundError",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "anyOf": [
+                    {
+                      "$ref": "#/components/schemas/MessageNotFoundErrorEncoded"
+                    },
+                    {
+                      "$ref": "#/components/schemas/SessionNotFoundErrorEncoded"
+                    }
+                  ]
+                }
+              }
+            }
+          },
+          "500": {
+            "description": "UnknownError",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/UnknownErrorEncoded"
+                }
+              }
+            }
+          }
+        },
+        "description": "Structured per-file diffs of the files a turn changed. A turn runs from the first prompt after the session was last idle until its next idle marker, so prompts steered in while it was busy belong to the same turn; `to` extends the range through a later turn. Compares the range's first recorded snapshot with its last; a step still running in the active session compares against the working copy. Ranges that span a location change are rejected. In sessions without any idle marker, a prompt's turn spans until the next user message.",
+        "summary": "Diff session turns"
+      }
+    },
     "/api/session/{sessionID}/inbox": {
       "get": {
         "tags": ["session"],
@@ -18486,6 +18625,38 @@
         "required": ["type", "id", "time", "status", "reason", "summary", "recent"],
         "additionalProperties": false
       },
+      "Session.Message.Idle": {
+        "type": "object",
+        "properties": {
+          "id": {
+            "type": "string",
+            "pattern": "^msg_"
+          },
+          "metadata": {
+            "type": "object"
+          },
+          "time": {
+            "type": "object",
+            "properties": {
+              "created": {
+                "type": "number"
+              }
+            },
+            "required": ["created"],
+            "additionalProperties": false
+          },
+          "type": {
+            "type": "string",
+            "enum": ["idle"]
+          },
+          "outcome": {
+            "type": "string",
+            "enum": ["succeeded", "failed", "interrupted"]
+          }
+        },
+        "required": ["id", "time", "type", "outcome"],
+        "additionalProperties": false
+      },
       "Session.Message.Info": {
         "anyOf": [
           {
@@ -18517,6 +18688,9 @@
           },
           {
             "$ref": "#/components/schemas/Session.Message.Compaction"
+          },
+          {
+            "$ref": "#/components/schemas/Session.Message.Idle"
           }
         ]
       },

packages/protocol/src/groups/session.ts

@@ -30,6 +30,7 @@ import { Model } from "@opencode-ai/schema/model"
 import { Location } from "@opencode-ai/schema/location"
 import { SessionEvent } from "@opencode-ai/schema/session-event"
 import { EventLog } from "@opencode-ai/schema/event-log"
+import { FileDiff } from "@opencode-ai/schema/file-diff"
 
 const ParentIDFilter = Schema.Union([
   Session.ID,
@@ -521,6 +522,31 @@ export const makeSessionGroup = <I extends HttpApiMiddleware.AnyId, S>(sessionLo
         }),
       ),
     )
+    .add(
+      HttpApiEndpoint.get("session.diff", "/api/session/:sessionID/diff", {
+        params: { sessionID: Session.ID },
+        query: Schema.Struct({
+          messageID: Schema.optional(SessionMessage.ID).annotate({
+            description: "User message whose turn to diff. Defaults to the turn of the newest user message.",
+          }),
+          to: Schema.optional(SessionMessage.ID).annotate({
+            description: "Later user message whose turn ends the range. Defaults to the turn of `messageID` alone.",
+          }),
+          context: Schema.NumberFromString.pipe(Schema.decodeTo(NonNegativeInt), Schema.optional).annotate({
+            description: "Unchanged lines around each hunk. Omit for full-file patches.",
+          }),
+        }),
+        success: Schema.Struct({ data: Schema.Array(FileDiff.Info) }),
+        error: [InvalidRequestError, MessageNotFoundError, SessionNotFoundError, UnknownError],
+      }).annotateMerge(
+        OpenApi.annotations({
+          identifier: "v2.session.diff",
+          summary: "Diff session turns",
+          description:
+            "Structured per-file diffs of the files a turn changed. A turn runs from the first prompt after the session was last idle until its next idle marker, so prompts steered in while it was busy belong to the same turn; `to` extends the range through a later turn. Compares the range's first recorded snapshot with its last; a step still running in the active session compares against the working copy. Ranges that span a location change are rejected. In sessions without any idle marker, a prompt's turn spans until the next user message.",
+        }),
+      ),
+    )
     .add(
       HttpApiEndpoint.get("session.inbox.list", "/api/session/:sessionID/inbox", {
         params: { sessionID: Session.ID },

packages/schema/src/session-message.ts

@@ -272,6 +272,18 @@ export const Compaction = Schema.Union([CompactionRunning, CompactionCompleted,
 )
 export type Compaction = CompactionRunning | CompactionCompleted | CompactionFailed
 
+/**
+ * Marks the Session going idle: every step since the previous marker belongs to
+ * one turn, including prompts steered in while it was busy. A shutdown does not
+ * record one, since the resumed execution continues the same turn.
+ */
+export interface Idle extends Schema.Schema.Type<typeof Idle> {}
+export const Idle = Schema.Struct({
+  ...Base,
+  type: Schema.tag("idle"),
+  outcome: Schema.Literals(["succeeded", "failed", "interrupted"]),
+}).annotate({ identifier: "Session.Message.Idle" })
+
 export const Info = Schema.Union([
   AgentSelected,
   ModelSelected,
@@ -283,6 +295,7 @@ export const Info = Schema.Union([
   Shell,
   Assistant,
   Compaction,
+  Idle,
 ]).annotate({ identifier: "Session.Message.Info" })
 export type Info =
   | AgentSelected
@@ -295,4 +308,5 @@ export type Info =
   | Shell
   | Assistant
   | Compaction
+  | Idle
 export type Type = Info["type"]

packages/server/src/handlers/session-error.ts

@@ -1,5 +1,6 @@
 import { Session } from "@opencode-ai/core/session"
-import { SessionNotFoundError, UnknownError } from "@opencode-ai/protocol/errors"
+import type { Snapshot } from "@opencode-ai/core/snapshot"
+import { MessageNotFoundError, SessionNotFoundError, UnknownError } from "@opencode-ai/protocol/errors"
 import { Effect } from "effect"
 
 export function missingSession(error: Session.NotFoundError) {
@@ -9,6 +10,14 @@ export function missingSession(error: Session.NotFoundError) {
   })
 }
 
+export function missingMessage(error: Session.MessageNotFoundError) {
+  return new MessageNotFoundError({
+    sessionID: error.sessionID,
+    messageID: error.messageID,
+    message: `Message not found: ${error.messageID}`,
+  })
+}
+
 export function failedMessageDecode(error: Session.MessageDecodeError) {
   const ref = `err_${crypto.randomUUID().slice(0, 8)}`
   return Effect.logError("failed to decode session message").pipe(
@@ -18,3 +27,16 @@ export function failedMessageDecode(error: Session.MessageDecodeError) {
     ),
   )
 }
+
+/** Snapshot repositories are host state clients cannot repair, so surface only a log reference. */
+export function failedSnapshot(operation: string, sessionID: Session.ID) {
+  return (error: Snapshot.Error) => {
+    const ref = `err_${crypto.randomUUID().slice(0, 8)}`
+    return Effect.logError(`failed to ${operation}`, { cause: error }).pipe(
+      Effect.annotateLogs({ ref, sessionID }),
+      Effect.andThen(
+        Effect.fail(new UnknownError({ message: "Unexpected server error. Check server logs for details.", ref })),
+      ),
+    )
+  }
+}

packages/server/src/handlers/session.ts

@@ -17,10 +17,9 @@ import {
   ServiceUnavailableError,
   SessionBusyError,
   SkillNotFoundError,
-  UnknownError,
 } from "@opencode-ai/protocol/errors"
 import { AbsolutePath } from "@opencode-ai/core/schema"
-import { failedMessageDecode, missingSession } from "./session-error"
+import { failedMessageDecode, failedSnapshot, missingMessage, missingSession } from "./session-error"
 
 const DefaultSessionsLimit = 50
 
@@ -212,15 +211,7 @@ export const SessionHandler = HttpApiBuilder.group(Api, "server.session", (handl
           return {
             data: yield* session.fork({ sessionID: ctx.params.sessionID, boundary: ctx.payload.boundary }).pipe(
               Effect.catchTag("Session.NotFoundError", missingSession),
-              Effect.catchTag(
-                "Session.MessageNotFoundError",
-                (error) =>
-                  new MessageNotFoundError({
-                    sessionID: error.sessionID,
-                    messageID: error.messageID,
-                    message: `Message not found: ${error.messageID}`,
-                  }),
-              ),
+              Effect.catchTag("Session.MessageNotFoundError", missingMessage),
               Effect.catchTag(
                 "Session.ForkEmptyError",
                 (error) => new InvalidRequestError({ message: error.message, kind: "empty_session" }),
@@ -448,32 +439,14 @@ export const SessionHandler = HttpApiBuilder.group(Api, "server.session", (handl
             files: ctx.payload.files,
           })
           return {
-            data: yield* session.revert.stage({ ...ctx.params, ...ctx.payload }).pipe(
-              Effect.catchTag("Session.NotFoundError", missingSession),
-              Effect.catchTag(
-                "Session.MessageNotFoundError",
-                (error) =>
-                  new MessageNotFoundError({
-                    sessionID: error.sessionID,
-                    messageID: error.messageID,
-                    message: `Message not found: ${error.messageID}`,
-                  }),
+            data: yield* session.revert
+              .stage({ ...ctx.params, ...ctx.payload })
+              .pipe(
+                Effect.catchTag("Session.NotFoundError", missingSession),
+                Effect.catchTag("Session.MessageNotFoundError", missingMessage),
+                Effect.catchTag("Session.BusyError", busySession),
+                Effect.catchTag("Snapshot.Error", failedSnapshot("stage session revert", ctx.params.sessionID)),
               ),
-              Effect.catchTag("Session.BusyError", busySession),
-              Effect.catchTag("Snapshot.Error", (error) => {
-                const ref = `err_${crypto.randomUUID().slice(0, 8)}`
-                return Effect.logError("failed to stage session revert", { cause: error }).pipe(
-                  Effect.andThen(
-                    Effect.fail(
-                      new UnknownError({
-                        message: "Unexpected server error. Check server logs for details.",
-                        ref,
-                      }),
-                    ),
-                  ),
-                )
-              }),
-            ),
           }
         }),
       )
@@ -481,23 +454,13 @@ export const SessionHandler = HttpApiBuilder.group(Api, "server.session", (handl
         "session.revert.clear",
         Effect.fn(function* (ctx) {
           yield* Effect.log("session.revert.clear", { sessionID: ctx.params.sessionID })
-          yield* session.revert.clear(ctx.params.sessionID).pipe(
-            Effect.catchTag("Session.NotFoundError", missingSession),
-            Effect.catchTag("Session.BusyError", busySession),
-            Effect.catchTag("Snapshot.Error", (error) => {
-              const ref = `err_${crypto.randomUUID().slice(0, 8)}`
-              return Effect.logError("failed to clear session revert", { cause: error }).pipe(
-                Effect.andThen(
-                  Effect.fail(
-                    new UnknownError({
-                      message: "Unexpected server error. Check server logs for details.",
-                      ref,
-                    }),
-                  ),
-                ),
-              )
-            }),
-          )
+          yield* session.revert
+            .clear(ctx.params.sessionID)
+            .pipe(
+              Effect.catchTag("Session.NotFoundError", missingSession),
+              Effect.catchTag("Session.BusyError", busySession),
+              Effect.catchTag("Snapshot.Error", failedSnapshot("clear session revert", ctx.params.sessionID)),
+            )
           return HttpApiSchema.NoContent.make()
         }),
       )
@@ -527,6 +490,22 @@ export const SessionHandler = HttpApiBuilder.group(Api, "server.session", (handl
           }
         }),
       )
+      .handle(
+        "session.diff",
+        Effect.fn(function* (ctx) {
+          return {
+            data: yield* session.diff({ sessionID: ctx.params.sessionID, ...ctx.query }).pipe(
+              Effect.catchTag("Session.NotFoundError", missingSession),
+              Effect.catchTag("Session.MessageNotFoundError", missingMessage),
+              Effect.catchTag(
+                "Session.TurnRangeError",
+                (error) => new InvalidRequestError({ message: error.message, field: error.field }),
+              ),
+              Effect.catchTag("Snapshot.Error", failedSnapshot("diff session turn", ctx.params.sessionID)),
+            ),
+          }
+        }),
+      )
       .handle(
         "session.inbox.list",
         Effect.fn(function* (ctx) {
@@ -642,15 +621,7 @@ export const SessionHandler = HttpApiBuilder.group(Api, "server.session", (handl
         Effect.fn(function* (ctx) {
           const message = yield* session.updateMessage({ ...ctx.params, content: ctx.payload.content }).pipe(
             Effect.catchTag("Session.NotFoundError", missingSession),
-            Effect.catchTag(
-              "Session.MessageNotFoundError",
-              (error) =>
-                new MessageNotFoundError({
-                  sessionID: error.sessionID,
-                  messageID: error.messageID,
-                  message: `Message not found: ${error.messageID}`,
-                }),
-            ),
+            Effect.catchTag("Session.MessageNotFoundError", missingMessage),
             Effect.catchTag("Session.BusyError", busySession),
             Effect.catchTag(
               "Session.MessageNotAssistantError",

packages/server/test/session-diff.test.ts

@@ -0,0 +1,98 @@
+import { expect, setDefaultTimeout } from "bun:test"
+import { Agent } from "@opencode-ai/core/agent"
+import { Bus } from "@opencode-ai/core/bus"
+import { Model } from "@opencode-ai/core/model"
+import { Provider } from "@opencode-ai/core/provider"
+import { Session } from "@opencode-ai/core/session"
+import { SessionEvent } from "@opencode-ai/core/session/event"
+import { SessionExecution } from "@opencode-ai/core/session/execution"
+import { SessionMessage } from "@opencode-ai/core/session/message"
+import { Money } from "@opencode-ai/schema/money"
+import { makeGlobalNode } from "@opencode-ai/util/effect/app-node"
+import { Effect, Layer } from "effect"
+import { tmpdir } from "../../core/test/fixture/tmpdir"
+import { it } from "../../core/test/lib/effect"
+import { ServerFetch } from "../src/fetch"
+
+setDefaultTimeout(30_000)
+
+it.live("serves turn diffs by user message with range validation", () =>
+  Effect.gen(function* () {
+    const tmp = yield* Effect.acquireDisposable(Effect.promise(() => tmpdir("opencode-session-diff-")))
+    const ids = { user: SessionMessage.ID.create(), assistant: SessionMessage.ID.create() }
+    // Deliver the prompt and one step the way the runner would, without a model.
+    const execution = Layer.effect(
+      SessionExecution.Service,
+      Effect.gen(function* () {
+        const bus = yield* Bus.Service
+        return SessionExecution.Service.of({
+          active: Effect.succeed(new Set()),
+          isActive: () => Effect.succeed(false),
+          resume: () => Effect.void,
+          wake: (sessionID) =>
+            Effect.gen(function* () {
+              yield* bus.publish(SessionEvent.InboxDelivered, { sessionID, inboxID: ids.user })
+              yield* bus.publish(SessionEvent.Step.Started, {
+                sessionID,
+                assistantMessageID: ids.assistant,
+                agent: Agent.defaultID,
+                model: { id: Model.ID.make("model"), providerID: Provider.ID.make("provider") },
+              })
+              yield* bus.publish(SessionEvent.Step.Ended, {
+                sessionID,
+                assistantMessageID: ids.assistant,
+                finish: "stop",
+                cost: Money.USD.zero,
+                tokens: { input: 0, output: 0, reasoning: 0, cache: { read: 0, write: 0 } },
+              })
+            }),
+          interrupt: () => Effect.succeed(false),
+          awaitIdle: () => Effect.void,
+        })
+      }),
+    )
+    const handler = yield* ServerFetch.make(
+      {
+        app: { version: "test-version" },
+        database: { path: ":memory:" },
+        fs: { filewatcher: false },
+        models: { fetch: false },
+      },
+      {
+        overrides: [
+          SessionExecution.node.replace(
+            makeGlobalNode({ service: SessionExecution.Service, layer: execution, deps: [Bus.node] }),
+          ),
+        ],
+      },
+    )
+    const request = (path: string, body?: unknown) =>
+      Effect.promise(async () => {
+        const response = await handler(
+          new Request(`http://opencode.local${path}`, {
+            method: body === undefined ? "GET" : "POST",
+            headers: body === undefined ? undefined : { "content-type": "application/json" },
+            body: body === undefined ? undefined : JSON.stringify(body),
+          }),
+        )
+        return { status: response.status, body: (await response.json()) as Record<string, unknown> }
+      })
+    const created = yield* request("/api/session", { location: { directory: tmp.path } })
+    const sessionID = Session.ID.make((created.body.data as { id: string }).id)
+    const diff = (query = "") => request(`/api/session/${sessionID}/diff${query}`)
+
+    expect(yield* diff()).toEqual({ status: 200, body: { data: [] } })
+    expect((yield* request(`/api/session/${sessionID}/prompt`, { id: ids.user, text: "prompt" })).status).toBe(200)
+    // Not a git repository, so steps record no snapshots and the turn has no diff.
+    expect(yield* diff(`?messageID=${ids.user}&context=3`)).toEqual({ status: 200, body: { data: [] } })
+    expect(yield* diff(`?messageID=${ids.assistant}`)).toMatchObject({
+      status: 400,
+      body: { _tag: "InvalidRequestError", field: "messageID" },
+    })
+    expect(yield* diff(`?messageID=${SessionMessage.ID.create()}`)).toMatchObject({
+      status: 404,
+      body: { _tag: "MessageNotFoundError" },
+    })
+    expect((yield* request(`/api/session/${Session.ID.create()}/diff`)).status).toBe(404)
+  }),
+)

packages/session-ui/src/timeline/projection.ts

@@ -16,7 +16,7 @@ export { TimelineRow, type PartGroup, type PartRef, type TimelineRowMap }
 
 export type ReasoningMode = "hidden" | "compact" | "full"
 
-type Notice = Exclude<SessionMessageInfo, { type: "user" | "assistant" | "shell" }>
+type Notice = Exclude<SessionMessageInfo, { type: "user" | "assistant" | "shell" | "idle" }>
 type Entry = { type: "assistant"; message: SessionMessageAssistant } | { type: "notice"; message: Notice }
 type Content = SessionMessageAssistant["content"][number]
 type GroupRow = Extract<TimelineRow.TimelineRow, { _tag: "AssistantPart" }>
@@ -765,7 +765,8 @@ function record(value: unknown): value is Record<string, unknown> {
 }
 
 function isNotice(message: SessionMessageInfo): message is Notice {
-  if (message.type === "user" || message.type === "assistant" || message.type === "shell") return false
+  if (message.type === "user" || message.type === "assistant" || message.type === "shell" || message.type === "idle")
+    return false
   if (message.type !== "synthetic") return true
   return !!message.description?.trim() || timelineNoticeRequired(message)
 }

packages/tui/src/routes/session/rows.ts

@@ -171,8 +171,18 @@ export function createSessionRows(sessionID: Accessor<string>, onSynced?: (sessi
   const appendPart = (ref: PartRef, part: AppendPart) =>
     setRows(
       produce((draft) => {
-        if (hasPart(draft, ref)) return
-        append(draft, ref, part, queuedStart(draft))
+        if (!hasPart(draft, ref)) {
+          append(draft, ref, part, queuedStart(draft))
+          return
+        }
+        if (part.type !== "reasoning" || part.time?.completed === undefined) return
+        const row = draft.find(
+          (row) =>
+            row.type === "group" &&
+            row.kind === "reasoning" &&
+            row.refs.some((item) => item.messageID === ref.messageID && item.partID === ref.partID),
+        )
+        if (row?.type === "group" && row.kind === "reasoning") row.completed = true
       }),
     )
 
@@ -250,7 +260,7 @@ export function createSessionRows(sessionID: Accessor<string>, onSynced?: (sessi
       if (event.data.sessionID === sessionID() && event.data.text.trim())
         appendPart(
           { messageID: event.data.assistantMessageID, partID: `reasoning:${event.data.ordinal}` },
-          { type: "reasoning" },
+          { type: "reasoning", time: { completed: event.created } },
         )
     }),
     data.on("session.tool.input.started", (event) => {
@@ -295,6 +305,7 @@ export function reduceSessionRows(messages: SessionMessageInfo[], inputs = new S
     ...messages.filter(isInput),
   ].reduce<SessionRow[]>((rows, message) => {
     if (message.type !== "assistant") {
+      if (message.type === "idle") return rows
       if (message.type === "synthetic" && !message.description?.trim()) return rows
       if (message.type === "compaction" && message.status === "completed" && usage) usage.previousTurnCache = undefined
       if (!pending.has(message.id)) completePrevious(rows)
@@ -437,17 +448,26 @@ export function resolvePart(message: SessionMessageAssistant, partID: string) {
   return message.content.filter((part) => part.type === match[1])[ordinal]
 }
 
-type AppendPart = { type: "text" } | { type: "reasoning" } | { type: "tool"; name: string }
+type AppendPart =
+  | { type: "text" }
+  | { type: "reasoning"; time?: { completed?: number } }
+  | { type: "tool"; name: string }
 
 function append(rows: SessionRow[], ref: PartRef, part: AppendPart, index = rows.length) {
   if (part.type === "reasoning") {
     const previous = rows[index - 1]
     if (previous?.type === "group" && previous.kind === "reasoning") {
       previous.refs.push(ref)
+      previous.completed &&= part.time?.completed !== undefined
       return
     }
     completePrevious(rows, index)
-    rows.splice(index, 0, { type: "group", kind: "reasoning", refs: [ref], completed: false })
+    rows.splice(index, 0, {
+      type: "group",
+      kind: "reasoning",
+      refs: [ref],
+      completed: part.time?.completed !== undefined,
+    })
     return
   }
   if (part.type === "tool" && exploration(part.name)) {

packages/web/src/content/docs/permissions.mdx

@@ -83,6 +83,10 @@ For most permissions, you can use an object to apply different actions based on
     "edit": {
       "*": "deny",
       "packages/web/src/content/docs/*.mdx": "allow"
+    },
+    "webfetch": {
+      "*": "ask",
+      "https://en.wikipedia.org/*": "allow"
     }
   }
 }
@@ -159,7 +163,7 @@ OpenCode permissions are keyed by tool name, plus a couple of safety guards:
 - `lsp` — running LSP queries (currently non-granular)
 - `question` — asking the user questions during execution
 - `webfetch` — fetching a URL (matches the URL)
-- `websearch` — web search (matches the query)
+- `websearch` — web search
 - `external_directory` — triggered when a tool touches paths outside the project working directory
 - `doom_loop` — triggered when the same tool call repeats 3 times with identical input
 

packages/www/openapi.json

@@ -1621,14 +1621,7 @@
             "content": {
               "application/json": {
                 "schema": {
-                  "anyOf": [
-                    {
-                      "$ref": "#/components/schemas/SessionNotFoundErrorEncoded"
-                    },
-                    {
-                      "$ref": "#/components/schemas/SessionNotFoundErrorEncoded"
-                    }
-                  ]
+                  "$ref": "#/components/schemas/SessionNotFoundErrorEncoded"
                 }
               }
             }
@@ -3249,6 +3242,152 @@
         "summary": "Get session context"
       }
     },
+    "/api/session/{sessionID}/diff": {
+      "get": {
+        "tags": ["session"],
+        "operationId": "v2.session.diff",
+        "parameters": [
+          {
+            "name": "sessionID",
+            "in": "path",
+            "schema": {
+              "type": "string",
+              "pattern": "^ses"
+            },
+            "required": true
+          },
+          {
+            "name": "messageID",
+            "in": "query",
+            "schema": {
+              "anyOf": [
+                {
+                  "type": "string",
+                  "pattern": "^msg_"
+                },
+                {
+                  "type": "null"
+                }
+              ],
+              "description": "User message whose turn to diff. Defaults to the turn of the newest user message."
+            },
+            "required": false
+          },
+          {
+            "name": "to",
+            "in": "query",
+            "schema": {
+              "anyOf": [
+                {
+                  "type": "string",
+                  "pattern": "^msg_"
+                },
+                {
+                  "type": "null"
+                }
+              ],
+              "description": "Later user message whose turn ends the range. Defaults to the turn of `messageID` alone."
+            },
+            "required": false
+          },
+          {
+            "name": "context",
+            "in": "query",
+            "schema": {
+              "anyOf": [
+                {
+                  "type": "string"
+                },
+                {
+                  "type": "null"
+                }
+              ],
+              "description": "Unchanged lines around each hunk. Omit for full-file patches."
+            },
+            "required": false
+          }
+        ],
+        "security": [],
+        "responses": {
+          "200": {
+            "description": "Success",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "type": "object",
+                  "properties": {
+                    "data": {
+                      "type": "array",
+                      "items": {
+                        "$ref": "#/components/schemas/FileDiff.Info"
+                      }
+                    }
+                  },
+                  "required": ["data"],
+                  "additionalProperties": false
+                }
+              }
+            }
+          },
+          "400": {
+            "description": "InvalidRequestError",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "anyOf": [
+                    {
+                      "$ref": "#/components/schemas/InvalidRequestErrorEncoded"
+                    },
+                    {
+                      "$ref": "#/components/schemas/InvalidRequestErrorEncoded"
+                    }
+                  ]
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "UnauthorizedError",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/UnauthorizedErrorEncoded"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "MessageNotFoundError | SessionNotFoundError",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "anyOf": [
+                    {
+                      "$ref": "#/components/schemas/MessageNotFoundErrorEncoded"
+                    },
+                    {
+                      "$ref": "#/components/schemas/SessionNotFoundErrorEncoded"
+                    }
+                  ]
+                }
+              }
+            }
+          },
+          "500": {
+            "description": "UnknownError",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/UnknownErrorEncoded"
+                }
+              }
+            }
+          }
+        },
+        "description": "Structured per-file diffs of the files a turn changed. A turn runs from the first prompt after the session was last idle until its next idle marker, so prompts steered in while it was busy belong to the same turn; `to` extends the range through a later turn. Compares the range's first recorded snapshot with its last; a step still running in the active session compares against the working copy. Ranges that span a location change are rejected. In sessions without any idle marker, a prompt's turn spans until the next user message.",
+        "summary": "Diff session turns"
+      }
+    },
     "/api/session/{sessionID}/inbox": {
       "get": {
         "tags": ["session"],
@@ -18486,6 +18625,38 @@
         "required": ["type", "id", "time", "status", "reason", "summary", "recent"],
         "additionalProperties": false
       },
+      "Session.Message.Idle": {
+        "type": "object",
+        "properties": {
+          "id": {
+            "type": "string",
+            "pattern": "^msg_"
+          },
+          "metadata": {
+            "type": "object"
+          },
+          "time": {
+            "type": "object",
+            "properties": {
+              "created": {
+                "type": "number"
+              }
+            },
+            "required": ["created"],
+            "additionalProperties": false
+          },
+          "type": {
+            "type": "string",
+            "enum": ["idle"]
+          },
+          "outcome": {
+            "type": "string",
+            "enum": ["succeeded", "failed", "interrupted"]
+          }
+        },
+        "required": ["id", "time", "type", "outcome"],
+        "additionalProperties": false
+      },
       "Session.Message.Info": {
         "anyOf": [
           {
@@ -18517,6 +18688,9 @@
           },
           {
             "$ref": "#/components/schemas/Session.Message.Compaction"
+          },
+          {
+            "$ref": "#/components/schemas/Session.Message.Idle"
           }
         ]
       },

packages/www/public/openapi.json

@@ -1621,14 +1621,7 @@
             "content": {
               "application/json": {
                 "schema": {
-                  "anyOf": [
-                    {
-                      "$ref": "#/components/schemas/SessionNotFoundErrorEncoded"
-                    },
-                    {
-                      "$ref": "#/components/schemas/SessionNotFoundErrorEncoded"
-                    }
-                  ]
+                  "$ref": "#/components/schemas/SessionNotFoundErrorEncoded"
                 }
               }
             }
@@ -3249,6 +3242,152 @@
         "summary": "Get session context"
       }
     },
+    "/api/session/{sessionID}/diff": {
+      "get": {
+        "tags": ["session"],
+        "operationId": "v2.session.diff",
+        "parameters": [
+          {
+            "name": "sessionID",
+            "in": "path",
+            "schema": {
+              "type": "string",
+              "pattern": "^ses"
+            },
+            "required": true
+          },
+          {
+            "name": "messageID",
+            "in": "query",
+            "schema": {
+              "anyOf": [
+                {
+                  "type": "string",
+                  "pattern": "^msg_"
+                },
+                {
+                  "type": "null"
+                }
+              ],
+              "description": "User message whose turn to diff. Defaults to the turn of the newest user message."
+            },
+            "required": false
+          },
+          {
+            "name": "to",
+            "in": "query",
+            "schema": {
+              "anyOf": [
+                {
+                  "type": "string",
+                  "pattern": "^msg_"
+                },
+                {
+                  "type": "null"
+                }
+              ],
+              "description": "Later user message whose turn ends the range. Defaults to the turn of `messageID` alone."
+            },
+            "required": false
+          },
+          {
+            "name": "context",
+            "in": "query",
+            "schema": {
+              "anyOf": [
+                {
+                  "type": "string"
+                },
+                {
+                  "type": "null"
+                }
+              ],
+              "description": "Unchanged lines around each hunk. Omit for full-file patches."
+            },
+            "required": false
+          }
+        ],
+        "security": [],
+        "responses": {
+          "200": {
+            "description": "Success",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "type": "object",
+                  "properties": {
+                    "data": {
+                      "type": "array",
+                      "items": {
+                        "$ref": "#/components/schemas/FileDiff.Info"
+                      }
+                    }
+                  },
+                  "required": ["data"],
+                  "additionalProperties": false
+                }
+              }
+            }
+          },
+          "400": {
+            "description": "InvalidRequestError",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "anyOf": [
+                    {
+                      "$ref": "#/components/schemas/InvalidRequestErrorEncoded"
+                    },
+                    {
+                      "$ref": "#/components/schemas/InvalidRequestErrorEncoded"
+                    }
+                  ]
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "UnauthorizedError",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/UnauthorizedErrorEncoded"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "MessageNotFoundError | SessionNotFoundError",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "anyOf": [
+                    {
+                      "$ref": "#/components/schemas/MessageNotFoundErrorEncoded"
+                    },
+                    {
+                      "$ref": "#/components/schemas/SessionNotFoundErrorEncoded"
+                    }
+                  ]
+                }
+              }
+            }
+          },
+          "500": {
+            "description": "UnknownError",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/UnknownErrorEncoded"
+                }
+              }
+            }
+          }
+        },
+        "description": "Structured per-file diffs of the files a turn changed. A turn runs from the first prompt after the session was last idle until its next idle marker, so prompts steered in while it was busy belong to the same turn; `to` extends the range through a later turn. Compares the range's first recorded snapshot with its last; a step still running in the active session compares against the working copy. Ranges that span a location change are rejected. In sessions without any idle marker, a prompt's turn spans until the next user message.",
+        "summary": "Diff session turns"
+      }
+    },
     "/api/session/{sessionID}/inbox": {
       "get": {
         "tags": ["session"],
@@ -18486,6 +18625,38 @@
         "required": ["type", "id", "time", "status", "reason", "summary", "recent"],
         "additionalProperties": false
       },
+      "Session.Message.Idle": {
+        "type": "object",
+        "properties": {
+          "id": {
+            "type": "string",
+            "pattern": "^msg_"
+          },
+          "metadata": {
+            "type": "object"
+          },
+          "time": {
+            "type": "object",
+            "properties": {
+              "created": {
+                "type": "number"
+              }
+            },
+            "required": ["created"],
+            "additionalProperties": false
+          },
+          "type": {
+            "type": "string",
+            "enum": ["idle"]
+          },
+          "outcome": {
+            "type": "string",
+            "enum": ["succeeded", "failed", "interrupted"]
+          }
+        },
+        "required": ["id", "time", "type", "outcome"],
+        "additionalProperties": false
+      },
       "Session.Message.Info": {
         "anyOf": [
           {
@@ -18517,6 +18688,9 @@
           },
           {
             "$ref": "#/components/schemas/Session.Message.Compaction"
+          },
+          {
+            "$ref": "#/components/schemas/Session.Message.Idle"
           }
         ]
       },