Merge branch 'master' into worktree/web-session-titles

# Conflicts:
#	apps/web/tests/smoke-real.e2e.ts
#	packages/client/connection/tests/fixture.spec.ts
#	packages/host/runtime/README.md
#	packages/host/runtime/src/api-proxy.ts

docs/core-data-structures/core.md

@@ -544,6 +544,6 @@ type SessionStartSource = 'startup' | 'resume' | 'clear' | 'compact'
 
 ## `ToolDefinition`
 
-The one pipeline-authoring type that is core: what every registered tool *is* — a model-facing `ToolSchema` plus an `execute` function and optional UI presenters. A tool author rarely constructs it by hand (the `defineTool` DSL builds it with typed args), but it is the contract the registry holds and the loop dispatches through.
+The one pipeline-authoring type that is core: what every registered tool *is* — a model-facing `ToolSchema` plus an `execute` function and optional final-content and UI callbacks. A tool author rarely constructs it by hand (the `defineTool` DSL builds it with typed args), but it is the contract the registry holds and the loop dispatches through.
 
 Its full fields, the `defineTool`/`ValueSchemaSpec`/`ParameterSchemaSpec` typed schema DSL, the `ToolExecution`/`ToolExecutionResult` waterfall shapes, and the tool-presentation UI vocabulary are on **[tools.md](tools.md)**.

docs/core-data-structures/pty.md

@@ -22,14 +22,14 @@ type PtySessionStatus =
 
 ## Backend and live session
 
-A backend owns how one registered type starts and detects readiness. `PtyService` publishes the returned session only after setup succeeds, then owns id authorization and cleanup. A backend session owns terminal state and captured-resource quiescence.
+A backend owns how one registered type starts and detects readiness. `PtyService` publishes the returned session only after setup succeeds, then owns id authorization and cleanup. A backend that cannot clean partial startup resources rejects with `PtyBackendCleanupError`, allowing disposal to retain the cleanup failure without replacing the caller's cancellation reason. A backend session owns terminal state and captured-resource quiescence.
 
 ```ts type-equiv
 /** Replaceable provider for one PTY session type. */
 interface PtyBackend {
   /** Stable type selected by {@link PtySpawnRequest.type}. */
   readonly type: string
-  /** Create an unpublished session or reject after cleaning partial resources. */
+  /** Create an unpublished session or reject after cleaning partial resources; cleanup failure uses {@link PtyBackendCleanupError}. */
   spawn(spec: PtyBackendSpawnSpec): Promise<PtyBackendSession>
 }
 ```

docs/core-data-structures/tasks.md

@@ -34,6 +34,11 @@ interface TaskStart {
   kind: TaskKind
   /** One-line model-facing label (the command; the delegation description). */
   label: string
+  /**
+   * Optional UTF-8 byte cap for each complete model-facing completion notice or
+   * output read, including control-surface status metadata.
+   */
+  outputLimitBytes?: number
   /**
    * Owning live agent. Access is fenced by its session id, and agent disposal
    * cancels and awaits the task. The instance must be the one currently
@@ -104,6 +109,8 @@ interface TaskSnapshot {
   kind: TaskKind
   /** The producer-supplied one-line label. */
   label: string
+  /** Producer-owned cap for complete model-facing notices and output reads. */
+  outputLimitBytes?: number
   /**
    * Owner session id used for authorization and correlation; absent for
    * unowned tasks. Completion listeners receive the exact {@link Agent}

docs/core-data-structures/tools.md

@@ -6,7 +6,7 @@ Source: [`packages/core/tools/src/index.ts`](../../packages/core/tools/src/index
 
 ## `ToolDefinition` — a registered tool
 
-A `ToolSchema` (the model-facing fields) plus a mandatory canonical output declaration, the `execute` function, host-only scheduler metadata, and optional UI presenters. The registry holds these; the loop dispatches calls through them. The registry's `schemas()` builds the model-facing `ToolSchema[]` by an explicit allowlist — `output`/`execute`/`timeoutMs`/`isConcurrencySafe`/`presentCall`/`presentResult` must never leak into a model request.
+A `ToolSchema` (the model-facing fields) plus a mandatory canonical output declaration, the `execute` function, host-only scheduler metadata, an optional final-content callback, and optional UI presenters. The registry holds these; the loop dispatches calls through them. The registry's `schemas()` builds the model-facing `ToolSchema[]` by an explicit allowlist — `output`/`execute`/`finalizeContent`/`timeoutMs`/`isConcurrencySafe`/`presentCall`/`presentResult` must never leak into a model request.
 
 ```ts type-equiv
 /** Tool-owned canonical output contract used after the body returns a JSON value. */
@@ -36,6 +36,18 @@ interface ToolDefinition extends ToolSchema {
    * @returns the canonical value declared by `output.schema`.
    */
   execute(args: unknown, exec: ToolRunContext): Promise<unknown>
+  /**
+   * Synchronous last-mile transform for model-facing content. The registry
+   * snapshots this callback when execution starts and invokes it exactly once
+   * for every normalized outcome, including pipeline failures that bypass
+   * `tools/post-execute`, immediately before lossless materialization.
+   * Returning `undefined` preserves the content; every other result field
+   * remains registry-owned. The callback must be total and must not throw.
+   * @param exec - immutable execution identity and arguments.
+   * @param result - complete normalized outcome before materialization.
+   * @returns replacement content, or `undefined` to preserve it.
+   */
+  finalizeContent?(exec: Readonly<ToolExecution>, result: Readonly<ToolExecutionResult>): ContentBlock[] | undefined
   /**
    * Cooperative tool-call timeout budget in milliseconds. Omit for no deadline.
    * Enforced by `@deepseek-ai/dsh-timeout-policy` (a `tools/execute` wrapper); it
@@ -79,7 +91,7 @@ interface ToolDefinition extends ToolSchema {
 }
 ```
 
-`execute` receives `args: unknown` — a raw `ToolDefinition` validates its own input. First-party tools don't write that by hand; they use `defineTool`, which validates and narrows the arguments, infers the body return from `output.schema`, and types both output projectors.
+`execute` receives `args: unknown` — a raw `ToolDefinition` validates its own input. First-party tools don't write that by hand; they use `defineTool`, which validates and narrows the arguments, infers the body return from `output.schema`, and types both output projectors. `finalizeContent` deliberately receives the immutable execution instead of typed arguments because invalid-input and outer pipeline failures reach it too; it may enforce a tool-owned content bound while preserving `isError`, canonical value, structured error identity, deferred contexts, and presentation metadata.
 
 ## The unified JSON-value schema DSL
 
@@ -155,7 +167,7 @@ interface ToolRestriction {
 
 ## Execution: extensible waterfalls plus monotonic policy
 
-`ctx.tools.execute()` accepts a caller-owned `ToolExecutionInput` with a required readonly `signal`, materializes its parsed JSON arguments once into a pipeline-owned `ToolExecution`, and runs that call through `tools/pre-execute` (the reorderable allow/deny/ask waterfall) → registered monotonic guards → `tools/execute` (around-dispatch wrappers) → `tools/post-execute` (inspect/replace the result) → `tools/result` (the immutable authoritative outcome). Only the `tools/execute` view may replace the required signal. The outcome is a `ToolExecutionResult`.
+`ctx.tools.execute()` accepts a caller-owned `ToolExecutionInput` with a required readonly `signal`, materializes its parsed JSON arguments once into a pipeline-owned `ToolExecution`, and runs that call through `tools/pre-execute` (the reorderable allow/deny/ask waterfall) → registered monotonic guards → `tools/execute` (around-dispatch wrappers) → `tools/post-execute` (inspect/replace the result) → optional definition-owned `finalizeContent` → `tools/result` (the immutable authoritative outcome). Only the `tools/execute` view may replace the required signal. The outcome is a `ToolExecutionResult`.
 
 ```ts type-equiv
 /** Opaque call identity that permits correlation without exposing mutable execution state. */
@@ -303,6 +315,8 @@ The result carries only the outcome. Call identity remains on the immutable `Too
 
 On success the registry snapshots and validates the body value, freezes it, and invokes the pure renderer plus the optional direct-surface metadata projector. It separately materializes the durable presentation fields immediately before `tools/result`; an invalid value, renderer/projector failure, or non-JSON presentation becomes a JSON-safe `isError`. The final live observer therefore sees the exact execution-local value beside fields safe for the later durable append.
 
+Before final content, the registry materializes the candidate result; a failure in content, structured error, additional context, or presentation metadata becomes a JSON-safe `isError` result that still reaches `finalizeContent`. The registry invokes that callback exactly once, then materializes and freezes the accepted result immediately before `tools/result`, so the observed live outcome is safe for the later durable `tool/result` append.
+
 Each interception waterfall returns a typed **Decision** (the idiom shared with the `agent/*` seams). `tools/pre-execute` listeners receive `(exec, next)` and return a `PreToolDecision`; `tools/execute` wrappers return a `ToolExecutionResult`; `tools/post-execute` listeners receive `(exec, result, next)` and return a `PostToolDecision`:
 
 ```ts type-equiv

docs/core-data-structures/user-interaction.md

@@ -58,14 +58,14 @@ interface AskUserQuestionRequest {
 
 ## Answer
 
-Providers return one answer per answered question id. `selected` contains selected option labels, and `custom` carries a free-form "Other" answer when the user typed one. When `custom` is present, `selected` is empty; custom text is an answer override, not a supplement to selected choices.
+Providers return one answer item per question id. `selected` contains selected option labels, and `custom` carries a free-form "Other" answer when the user typed one. When `custom` is present, `selected` is empty; custom text is an answer override, not a supplement to selected choices. A UI may also use an item with empty `selected` and no `custom` to preserve a skipped question in an otherwise completed batch.
 
 ```ts type-equiv
 /** Answer to one question. */
 interface AskUserQuestionAnswerItem {
   /** The answered question id. */
   id: string
-  /** Selected option labels. Empty when the answer is purely custom text. */
+  /** Selected option labels. Empty for custom or unanswered choices. */
   selected: string[]
   /** Optional free-text "Other" answer. */
   custom?: string