[WRONG BRANCH] fix(combos): bound preflight retained chunks

[luvs01]

Motivation

• The combo SSE preflight path buffered every upstream read as a separate Uint8Array, allowing a malicious upstream to amplify allocations via many tiny chunks and cause an availability DoS.
• The intent is to limit retained memory and allocation count while preserving the ability to commit and replay an already-read prefix for safe failover.

Description

• Add a per-chunk cap COMBO_STREAM_PREFLIGHT_MAX_CHUNKS = 1024 and treat either the byte cap or the chunk-count cap as a commit boundary.
• When a cap is hit, commit the current combo target and call replayBufferedResponse with the already-read unsliced next chunk so no extra copies are retained.
• Update the preflight comment to reflect the dual cap and preserve existing replay semantics.
• Add a focused regression test in tests/combo-stream-preflight.test.ts that verifies preflight stops buffering before consuming an excessive tiny-chunk prefix and that the replayed response preserves the full byte stream.

Testing

• ./node_modules/.bin/bun test tests/combo-stream-preflight.test.ts — passed (5 passed, 0 failed).
• bun run typecheck — succeeded.
• bun run privacy:scan — passed.
• bun run test (full suite) — the broader test run surfaced unrelated pre-existing Lab/timeout issues; testing was stopped after the focused combo preflight tests passed successfully.

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Codex Task

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⏳ DRAFT

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

What to do

• 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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[chatgpt-codex-connector]

Commit as soon as the chunk cap is reached

When the upstream delivers exactly 1,024 tiny chunks and then pauses, the 1,024th chunk is retained but the chunk-count boundary is not checked again before the next reader.read(). Preflight therefore waits indefinitely for a 1,025th chunk instead of committing and exposing the buffered stream to the client. Include buffered.length >= COMBO_STREAM_PREFLIGHT_MAX_CHUNKS in the post-feed commit condition, and cover a source that stalls immediately after the boundary.

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