fix(tools): preserve bounded fallback guidance

.agents/notes/implemented/architecture/2026-06-20-generic-long-running-tool-runtime.md

@@ -75,7 +75,7 @@ Stream reads share one task-scoped consuming cursor because the owning model is
 
 The system prompt tells the model to retain task ids, continue independent work instead of busy-polling or duplicating a running task, collect relevant tasks before its final answer, and kill work that no longer matters. Completion injects a logged `context/message` into the exact owner's session; it becomes durable context for the next request but does not wake an idle agent.
 
-The runtime marks a terminal task `reported` when a read or wait delivers it, when a live waiter has claimed delivery at settlement, or when the model explicitly kills it. Reported tasks do not inject redundant completion notices. Listener failures are logged independently, do not stop later listeners, and are not awaited by waiters or teardown. When a snapshot carries `outputLimitBytes`, `dsh-tool-tasks` preserves UTF-8 boundaries and reuses an existing producer truncation marker rather than duplicating it. Reads reserve status suffixes and retain the output tail; completion notices reserve the stable `background task <id>` prefix and `task_output` instruction before truncating variable kind, label, status, or detail, so the minimum PTY cap still identifies the task to collect. The task surface resolves the caller-visible producer cap in a prepended pre-execute listener before policy can deny or short-circuit dispatch, then applies it through the task definitions' last-mile `finalizeContent` callback so normalized tool errors, outer pipeline failures, and single-text policy results cannot escape the bound; deliberately structured multi-block policy results retain policy ownership of their shape and size.
+The runtime marks a terminal task `reported` when a read or wait delivers it, when a live waiter has claimed delivery at settlement, or when the model explicitly kills it. Reported tasks do not inject redundant completion notices. Listener failures are logged independently, do not stop later listeners, and are not awaited by waiters or teardown. When a snapshot carries `outputLimitBytes`, `dsh-tool-tasks` preserves UTF-8 boundaries and reuses an existing producer truncation marker rather than duplicating it. Reads reserve status suffixes and retain the output tail; completion notices reserve the stable `background task <id>` prefix and `task_output` instruction before truncating variable kind, label, status, detail, or the truncation marker itself, so the minimum PTY cap still identifies the task to collect. The task surface resolves the caller-visible producer cap in a prepended pre-execute listener before policy can deny or short-circuit dispatch, then applies it through the task definitions' last-mile `finalizeContent` callback so normalized tool errors, outer pipeline failures, and single-text policy results cannot escape the bound; deliberately structured multi-block policy results retain policy ownership of their shape and size.
 
 ## Producer opt-in
 

.agents/notes/implemented/architecture/2026-07-12-agent-scope-runtime-design.md

@@ -218,7 +218,7 @@ A fresh registry-assigned Symbol provides collision-free execution identity with
 
 Arguments are materialized once where model/tool JSON enters the pipeline. Pre-, around-, and post-execute listeners operate on the typed execution and decisions. Call ID correlation, approval, monotonic guards, and Code Mode nesting remain explicit relational checks.
 
-After post-execute or outer pipeline normalization, the registry invokes the call's snapshotted optional `ToolDefinition.finalizeContent` callback, then materializes and freezes the accepted final result once. The callback may replace only content, so structured error identity, contexts, and metadata remain registry-owned even when a tool enforces a last-mile result bound. Every synchronous `tools/result` observer receives that exact committed object, and observer failures are contained individually. An outer pipeline failure is normalized before final content, so observers can discard staged work against the same authoritative boundary.
+After post-execute or outer pipeline normalization, the registry losslessly snapshots the candidate result, converting a snapshot failure into an ordinary error, invokes the call's snapshotted optional `ToolDefinition.finalizeContent` callback, then materializes and freezes the accepted final result once. The callback may replace only content, so structured error identity, contexts, and metadata remain registry-owned even when a tool enforces a last-mile result bound. Every synchronous `tools/result` observer receives that exact committed object, and observer failures are contained individually. An outer pipeline or candidate-snapshot failure is normalized before final content, so observers can discard staged work against the same authoritative boundary.
 
 ### The assembly waterfall owns the final model-visible composition
 

.agents/notes/implemented/architecture/2026-07-19-cooperative-tool-cancellation.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write
-2026-07-19-cooperative-tool-cancellation.md: e86c087de53fe742436bc01571394657a0a5c9ac
-2026-07-19-cooperative-tool-cancellation.zh.md: 91b91b3894dbdc56d57f4819ff4c567305ecfc9d
+2026-07-19-cooperative-tool-cancellation.md: be237f6ca9475699bb4af76896772a1a7409033d
+2026-07-19-cooperative-tool-cancellation.zh.md: 9ad212c2073063ccb0c838c08ab8f89c9285b26b

.agents/notes/implemented/architecture/2026-07-19-cooperative-tool-cancellation.md

@@ -36,7 +36,7 @@ An around-dispatch wrapper may replace `exec.signal` for its delegated lifetime
 
 ### Pre-aborted entry short-circuits after materialization
 
-The registry first creates the call token, snapshots the visible definition's optional final-content callback, and losslessly snapshots and freezes the arguments. A materialization failure wins even when the caller signal is already aborted. After successful materialization, a pre-aborted signal skips `tools/pre-execute`, approval, `tools/execute`, `tools/post-execute`, and the tool body, then passes `ABORTED_BEFORE_DISPATCH` through that content-only callback before publishing exactly one frozen authoritative `tools/result`.
+The registry first creates the call token, snapshots the visible definition's optional final-content callback, and losslessly snapshots and freezes the arguments. An argument-materialization failure wins even when the caller signal is already aborted. Before final content, the registry also losslessly snapshots the candidate result and converts a result-snapshot failure into an ordinary error, so the callback can still enforce its content invariant. After successful argument materialization, a pre-aborted signal skips `tools/pre-execute`, approval, `tools/execute`, `tools/post-execute`, and the tool body, then passes `ABORTED_BEFORE_DISPATCH` through that content-only callback before publishing exactly one frozen authoritative `tools/result`.
 
 ### Started work still reaches quiescence
 

.agents/notes/implemented/architecture/2026-07-19-cooperative-tool-cancellation.zh.md

@@ -36,7 +36,7 @@ Status: implemented
 
 ### 进入时已中止会在物化后短路
 
-注册表先创建调用 token，对可见工具定义的可选 `finalizeContent` callback 做快照，并对参数进行无损快照和冻结。即使调用方信号已经中止，参数物化失败仍优先返回。物化成功后，进入时已中止的信号会跳过 `tools/pre-execute`、审批、`tools/execute`、`tools/post-execute` 和工具主体，然后先由该仅处理内容的 callback 处理 `ABORTED_BEFORE_DISPATCH`，再发布且只发布一次冻结的权威 `tools/result`。
+注册表先创建调用 token，对可见工具定义的可选 `finalizeContent` callback 做快照，并对参数进行无损快照和冻结。即使调用方信号已经中止，参数物化失败仍优先返回。在最终内容处理之前，注册表还会对候选结果进行无损快照，并把结果快照失败转换为普通错误，从而使该 callback 仍能保证其内容不变量成立。参数物化成功后，进入时已中止的信号会跳过 `tools/pre-execute`、审批、`tools/execute`、`tools/post-execute` 和工具主体，然后先由该仅处理内容的 callback 处理 `ABORTED_BEFORE_DISPATCH`，再发布且只发布一次冻结的权威 `tools/result`。
 
 ### 已启动工作仍必须完全停稳
 

.agents/notes/implemented/feature/2026-06-30-interception-seams.md

@@ -26,10 +26,10 @@ Every call follows `tools/pre-execute` → guards → `tools/execute` → dispat
 - **`ctx.tools.guard()`** installs synchronous scope-aware policy after the whole pre-execute waterfall. A guard may deny or abstain, never force-allow, so listener ordering cannot resurrect an operation that a final invariant forbids.
 - **`tools/execute`** is the around-dispatch waterfall for timeout, retry, and metrics plugins. A wrapper delegates to core dispatch with `next()`, may replace and restore the required `exec.signal` before doing so but cannot remove it, and receives the already-normalized result of a thrown or unknown tool; returning its own valid result short-circuits dispatch.
 - **`tools/post-execute`** is the inspect/transform waterfall. Its `PostToolDecision` accepts, blocks with feedback, optionally replaces content, or attaches `additionalContexts`. The returned decision is the supported cross-tool transform channel.
-- **`ToolDefinition.finalizeContent`** is an optional synchronous, total, content-only boundary snapshotted with the visible definition at call creation. It runs exactly once after the registry has normalized the final outcome, including pre-, around-, or post-listener failures that bypass later waterfalls. It may replace `content` or preserve it with `undefined`, but cannot rewrite `isError`, structured error identity, contexts, or presentation metadata. This is where a tool enforces its own last-mile content invariant without converting policy failures into weaker block decisions.
+- **`ToolDefinition.finalizeContent`** is an optional synchronous, total, content-only boundary snapshotted with the visible definition at call creation. It runs exactly once after the registry has normalized and losslessly snapshotted the candidate outcome, including pre-, around-, or post-listener failures that bypass later waterfalls and errors discovered while snapshotting another result field. It may replace `content` or preserve it with `undefined`, but cannot rewrite `isError`, structured error identity, contexts, or presentation metadata. This is where a tool enforces its own last-mile content invariant without converting policy failures into weaker block decisions.
 - **`tools/result`** is the synchronous contained notification after every transform, lossless-JSON materialization, and the outer error boundary. It receives the same frozen execution identity and an immutable snapshot of the authoritative result; observer failures are contained per listener and cannot change or reject `ToolRegistry.execute()`'s returned outcome.
 
-Core dispatch and the tool body sit inside normalization boundaries, so tool, listener, malformed-result, non-JSON result, and identity-shape failures resolve as JSON-safe `isError` results rather than escaping the turn. A post-execute listener can therefore inspect a thrown tool; definition-owned final content invariants also cover outer pipeline failures; and a final observer sees exactly what the caller receives and the session log can persist.
+Core dispatch and the tool body sit inside normalization boundaries, so tool, listener, malformed-result, non-JSON result, and identity-shape failures resolve as JSON-safe `isError` results rather than escaping the turn. A post-execute listener can therefore inspect a thrown tool; definition-owned final content invariants also cover outer pipeline and candidate-snapshot failures; and a final observer sees exactly what the caller receives and the session log can persist.
 
 **`TurnEndReason.rejected`** (`dsh-session`): a zero-step turn whose claimed prompt was blocked by `prompt-submit`.