Merge remote-tracking branch 'origin/docs/i18n-batch-core' into worktree/pr344-retarget-stack

# Conflicts:
#	docs/core-data-structures/session-query.md
#	scripts/type-equiv.manifest.json

docs/core-data-structures/tools.md

@@ -8,7 +8,7 @@ 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. */
@@ -38,6 +38,18 @@ 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
@@ -81,7 +93,7 @@ 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
 
@@ -157,7 +169,7 @@ 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. */
@@ -305,6 +317,8 @@ 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