[yujiachen-y]

Change

mcode exec --timeout adds an execution budget reminder to model requests. The reminder was request-only: it was appended after the last user message and never written to history. The Anthropic adapter puts the conversation cache breakpoint on the last user message, so every request that carried a reminder wrote its cache entry ending at a message the next request no longer contained. Outside the final two minutes this cost about one step of re-written context per reminder. In the final two minutes every request carried a reminder, so cache reads stopped advancing and the uncached tail grew with every step; once it falls out of the provider's lookback window, every request re-writes the whole conversation history, exactly when the run is shortest on time.

The reminder could not simply be written to history because runBeforeLLM ended the decision pipeline at the first appendMessage, which would have starved the background, session identity and todo reminders. This PR therefore changes both:

• Before-LLM pipeline (agent-core): appendMessage decisions accumulate instead of ending the pipeline, and later hooks see the registered markers. Everything is committed once after the pipeline: at most one durable replacement carrying the before-current-user markers, then every tail marker in registration order with a single history flush. A durable replaceMessages after a registered append fails closed (production registers compaction before every appending reminder). This also stops the existing background reminder from skipping the request filter, session identity and todo reminders.

• Multiple placed markers: compaction commit metadata and the canonical tail validation accept more than one marker before the current user through a runner-owned placedMarkerCount. Existing metadata without it is read as one marker.

• Execution budget reminder: it is now a hidden durable custom marker (execution_budget_reminder, display: false) appended like the other reminders, so each provider request is an append-only extension of the previous one. The model-visible text, thresholds and position are unchanged. Progress is derived from the latest reminder of the same deadline in history instead of hook instance state: a repeated request does not duplicate it, a compaction that summarized reminders away announces the budget again, and in the final two minutes a reminder is only appended when its 10-second text changes.

• Tests: the BYOK cancellation tests run mcode exec --timeout, so their persisted history now also contains the hidden budget reminder; they assert it explicitly.

Labels: bug, cli, perf:full (changes history construction in the tool loop).

Validation

• New execution-budget-cache-prefix.integration.test.ts runs a real PiTurnRunner tool loop with the budget hook and a fake clock across the first announcement, quiet requests, the 50% and 25% thresholds and the final two minutes (including two requests in the same 10-second step), and asserts that every provider request starts with the previous one. It fails on main at the first reminder request and passes with this change.
• Reverse checks on this branch: restoring the main reminder makes 22 tests fail (integration 1, reminder unit 12, executor 9); restoring the main runBeforeLLM makes 7 executor tests fail. Both pass again after restoring this change.
• Focused Vitest: execution budget reminder 13/13, cache-prefix integration 1/1, executor 159/159, context compaction (including new two-marker metadata cases), session identity reminder — 246 passed.
• pnpm verify (full profile, darwin/arm64, Node 22.22.2) on 156f206: PASS for every applicable gate (source, tsconfig, export preview, release tools, TUI lint, typecheck, build, standalone, artifact, capabilities, status contract, smoke, BYOK, policy, sandbox); test:windows and test:release-package are skipped on this platform. Run with the proxy environment variables unset, because this machine's NODE_USE_ENV_PROXY makes child Node processes print warnings that the unrelated local-bash-output test counts as output lines.
• Live check (offline evidence above is the gate): the same change, run through mcode exec --timeout 3m against an Anthropic-protocol model, kept the previous request's breakpoint prefix on every request (12/12) and cache reads advanced on every request in the final two minutes (cache writes stayed at 105–242 tokens per request); the request-only reminder lost the prefix on every reminder request (6/10) and cache reads stayed flat while cache writes grew 105 → 500 tokens over the final-window requests. This was a single 3-minute sample with a ~19k-token context.
• Performance: perf:full requested.
• NOT RUN: Windows and Linux locally (covered by CI), long runs whose uncached tail exceeds the provider lookback window, and live providers other than the Anthropic protocol.

Publication and contribution checks

• I have permission to contribute these changes under the existing licenses applicable to the changed files/packages; imported material and its provenance are identified and existing notices are preserved.
• No credentials, account data, real user content, internal source history or private review material is included.
• Added/removed source files were reviewed before regenerating release/public-source.json; new tests are declared in test/vitest-suites.json where applicable.
• Shared English/Chinese documentation and capability/verification records are updated where applicable. Mock/offline results are not described as live-service acceptance.

Maintainer handoff

Publication scope or license changes (if any): none.

Shared-source port: complete.

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