[WRONG BRANCH] fix(responses): enforce aggregate UTF-16 backlog budget for adapter event queue

[luvs01]

Motivation

• A recent coalescing change let adjacent deltas merge before the single maxBacklog check, which permitted 1,024 coalesced slots to each grow to 64 Ki UTF-16 code units and amplified per-turn retained payload far beyond the intended safety valve.
• That regression makes a malicious or verbose upstream able to hold many megabytes per turn and, with many concurrent turns, amplify to process-wide memory exhaustion.

Description

• Add an aggregate UTF-16 code-unit backlog budget (DEFAULT_MAX_BACKLOG_CODE_UNITS) and per-queue tracking to account for retained string payloads, including nested string fields. 【F:src/adapters/run-turn-queue.ts†L12-L31】
• Introduce retainedStringCodeUnits and retainedEventStringCodeUnits helpers and a maxBacklogCodeUnits queue option to compute and cap retained string payload before insertion. 【F:src/adapters/run-turn-queue.ts†L16-L31】【F:src/adapters/run-turn-queue.ts†L84-L93】
• Enforce the aggregate payload budget before coalescing or pushing an event, preserve the existing item-count maxBacklog cap, abort the producer via the configured onBacklogExceeded callback on breach, and deduct retained code units when events are consumed. 【F:src/adapters/run-turn-queue.ts†L123-L160】【F:src/adapters/run-turn-queue.ts†L156-L164】
• Add focused regression tests that exercise (1) coalesced-delta overflow against the aggregate budget, (2) rejection of an oversized individual event, and (3) budget recovery when buffered events are consumed. 【F:tests/run-turn-queue.test.ts†L116-L164】

Testing

• ✅ Ran the focused queue tests with bun test tests/run-turn-queue.test.ts, and all tests passed.【F:tests/run-turn-queue.test.ts†L1-L10】
• ✅ Ran type checking with bun run typecheck and the code compiles cleanly.
• ✅ Ran repository privacy checks with bun run privacy:scan and they passed.
• ⚠️ Attempted a full bun run test of the entire suite but the repository-wide parallel run exposed unrelated pre-existing Lab/auth test failures and timeouts; the focused queue tests and typecheck passed and validate the added behavior.

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Codex Task

[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-08-30T05:43:57.061109Z	e0d02dd	PR opened

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[github-actions]

⏳ DRAFT

• wrong target branch (main); retarget to dev.

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• Retarget this PR to dev — all contributions go to dev.

Its title has been prefixed with [WRONG BRANCH].
This pull request was already a draft. Its draft status will be preserved after every issue above is resolved.

[chatgpt-codex-connector]

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Reviewed commit: e0d02dd81a

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[chatgpt-codex-connector]

Track only strings retained after delta coalescing

When Kiro emits adjacent phased text_delta events, backlogCodeUnits counts the repeated phase string on every push before coalescing, even though the merged queue item retains that field only once. Dequeueing consequently subtracts only one copy and leaves phantom backlog units, so a long stream of commentary or final_answer deltas can eventually abort despite the actual buffered payload remaining below the limit; with maxBacklogCodeUnits: 12, for example, two one-character commentary deltas should merge into a 12-unit event but the second is rejected. Update the accounting from the post-coalescing retained value, or remove the duplicated phase charge when replacing the tail.

AGENTS.md reference: src/AGENTS.md:L19-L19

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