fix(cursor): refund spare envelope bytes to clipped invocation arguments - #4543
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The 2 KiB per-call cap on the arguments named inside a replayed tool-result envelope is charged while the envelope is still being built, so it cost a call 2 KiB whether or not anything else wanted those bytes. In a small replay nearly the whole 192-root / 512 KiB envelope went unused and the cap still bit: a 4,693-byte successful write_file lost its tail inside a 6,011-byte replay, and because the result text does not repeat the argument, the model could no longer see what it had just written. Add a second pass after the root set is assembled and before it is stored. It spends only leftover aggregate bytes, newest tool result first, skips a root whose own output was already elided, and never drops, shrinks or reorders a retained root. The cap itself is unchanged and still decides admission on its 2 KiB prefix, so a 600 KiB argument stays clipped rather than evicting the output it describes. The gate is echoToolResultInRoot, not externalModel: native composer-2.5 echoes results into roots without being an external wire model, so the narrower gate would have left the one native model with clipped invocation lines capped for no reason. The widening uses the callback form of String.prototype.replace, because serialized arguments routinely contain $&, $' and $1, which the string form would expand into the surrounding match. Closes #4516
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Included review availability: Your plan provides up to 10 included reviews per hour; 3 remain after this review. 📝 WalkthroughWalkthroughCursor replay now restores clipped tool-call arguments when unused aggregate capacity remains. The pass preserves retained roots, ordering, output, checkpoint bytes, and replay limits. Tests cover restoration rules, native ChangesCursor replay argument restoration
Priority: ➖ Normal Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Bug fix · Severity of issue fixed: Medium 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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| // Refund envelope bytes the assembled set left unused to invocation arguments the per-call cap | ||
| // clipped. Gated on `echoToolResultInRoot`, not `externalModel`: native `composer-2.5` echoes its | ||
| // results into roots without being an external wire model, so the narrower gate would leave the one | ||
| // native model that has clipped invocation lines capped for no reason (#4516). | ||
| if (echoToolResultInRoot && replayedCalls) { | ||
| selected = restoreClippedInvocationArguments( |
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This changes behavior under src/adapters/, but the commit updates only structure/providers/cursor.md; structure/INDEX.md also maps this area to the runtime, byte-accounting, Responses, transport-inventory, inbound-compatibility, chat-compatibility, and adapter-registry contracts. Update each mapped document in this change so their descriptions remain synchronized with the new replay-budget behavior.
AGENTS.md reference: structure/AGENTS.md:L49-L50
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| const widened = entry.text.replace(clippedLine, () => `invoked: ${name} with ${full}`); | ||
| const candidate = rootBlobCandidate( | ||
| toolResultRootPayload(widened), | ||
| "toolResult", | ||
| { messageIndex: entry.messageIndex, text: widened }, |
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When two consecutive identical tool-result roots contain a clipped invocation and spare budget exists, pushDeduped stores its repetition-count annotation only in the candidate payload while leaving entry.text unannotated (src/adapters/cursor/protobuf-request.ts:325-331). Rebuilding the root from entry.text here therefore replaces the annotated root with an unannotated one, silently undoing the repetition breaker for the two-repeat case. Widen the actual rendered payload or keep the candidate's text synchronized, and add a duplicate-result regression test.
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리뷰 · 우선순위 73 / 80이 PR은 Cursor 어댑터가 이미 끝난 도구 호출의 인자(arguments)를 다시 보여줄 때, 2 KiB 한도 때문에 잘린 부분을 봉투에 남은 여유 바이트로 되돌려 주는 수리입니다. 지금 로컬 현재 수리 방식은 파일은 세 개입니다. 검증은 로컬 제품 스위트·typecheck·build·install을 돌리지 않았고, hosted Cross-platform CI 런 34774438316(exact head 라인 701-710 - 메인테이너의 판단이 필요한 지점
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Actionable comments posted: 1
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Inline comments:
In `@src/adapters/cursor/protobuf-request.ts`:
- Line 1043: Update the duplicate replacement around pushDeduped so
rootBlobCandidate receives the marked text rather than the unmarked opts.text,
ensuring serialized, data, and byteLength are recalculated from that same marked
value. Add a regression test covering duplicate tool-result roots with clipped
arguments, asserting that full arguments, result output, and the repetition
marker survive restoration.
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src/adapters/cursor/protobuf-request.tsstructure/providers/cursor.mdtests/providers/cursor/cursor-tool-result-invocation.test.ts
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request.rawMessages is readonly OcxMessage[]; the new second pass declared a mutable OcxMessage[] parameter, which strict typecheck rejects (TS4104). The pass only reads the array, so widen the parameter instead of copying.
An adversarial counter-read of the restoration pass found the real defect one layer down. pushDeduped builds the collapsed root's wire payload from the marked text but stored the UNMARKED text in the candidate's `text` field, so every consumer that rebuilds a root from `text` silently deleted the "produced N times in a row" note: truncateToolResultBlob already did, and the new invocation restoration did too. That note is the repetition breaker's per-entry half, so losing it re-primes the self-reinforcing loop the breaker exists to end. Store the marked text, which makes `text` a true mirror of the stored payload for the first time, and fixes the truncation path by the same change. Also anchor the restoration's search on the preceding newline. toolResultToText always emits the invocation after the [tool_result], call_id: and name: lines, so the real line is never first; name: renders the result's tool name, which nothing sanitizes, so an unanchored search could be satisfied by a crafted tool name and rewrite that header instead of the invocation. The regression test fails with the pushDeduped change reverted and passes with it.
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Inline comments:
In `@src/adapters/cursor/protobuf-request.ts`:
- Line 1046: Update the invocation-restoration logic around clippedLine and the
first replace so it matches the final structural invocation line before
“\noutput:\n”, rather than allowing a newline-containing name to match the tool
header. Preserve argument restoration for the real invocation, or consistently
reject newline characters in both call and result names.
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src/adapters/cursor/protobuf-request.tstests/providers/cursor/cursor-tool-result-invocation.test.ts
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| // `[tool_result]`, `call_id:` and `name:` lines, so the real line is never first — and | ||
| // `name:` renders the RESULT's tool name, which nothing sanitizes, so an unanchored search could | ||
| // be satisfied by a crafted tool name and rewrite that header instead of the invocation. | ||
| const clippedLine = `\ninvoked: ${name} with ${clipped}`; |
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🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win
Match the invocation line structurally before restoring arguments.
namespacedToolName() returns an unnamespaced name unchanged (src/types/tools.ts:30-32). toolResultToText() inserts message.toolName into the name: header before the real invocation line (src/adapters/cursor/protobuf-request.ts:1157-1169). MCP discovery copies tool.name without newline validation (src/adapters/cursor/mcp-manager.ts:200-207).
A result name containing \ninvoked: ${name} with ${clipped} can therefore create the anchored match inside the header. The first replace() at src/adapters/cursor/protobuf-request.ts:1052 widens that header and leaves the real invocation clipped. Select the final matching invocation line before \noutput:\n, or reject newlines in both call and result names.
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In `@src/adapters/cursor/protobuf-request.ts` at line 1046, Update the
invocation-restoration logic around clippedLine and the first replace so it
matches the final structural invocation line before “\noutput:\n”, rather than
allowing a newline-containing name to match the tool header. Preserve argument
restoration for the real invocation, or consistently reject newline characters
in both call and result names.
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review. Visit https://docs.coderabbit.ai/cli?utm_source=ghpr.
The refund leaves those two fixtures alone because restoring a 600 KiB argument costs more than the whole envelope, so cost > spare is always true there. That is a size-dependent skip, not a rule that the line stays clipped: an argument over the cap but well under the envelope is restored by design. Anyone shrinking those fixtures to speed them up would silently convert them from tests of the cap into tests of the refund, which is the one reading that would make them vacuous.
|
Integrating through the maintainer self-integration path in MAINTAINERS.md and recording that choice here. Exact-head evidence: Cross-platform CI run 34776361364 completed success at the current head. Local product suite, typecheck, build and install NOT RUN. Worth naming: an earlier head of this branch failed the On the change: the per-call 2 KiB argument cap was applied at envelope construction and never revisited, so a completed call could lose its tail inside a replay that used a fraction of the 192-root, 512 KiB envelope. A second pass now spends only leftover aggregate bytes, newest result first, skipping roots that already lost their own output, and never evicting a retained root. The cap itself is untouched; the two existing 600 KiB tests that prove it still bites under pressure remain unchanged and green. This claims nothing about #3506 causation. The four rejected patches there were all under the cap. |
Five regressions for the invocation refund landed in #4543. - A just-over-cap argument (~2,117 bytes against the 2,048 cap) must come back byte-exact. The existing fixture is 4,600 bytes, where thousands of spare bytes surround the decision and an off-by-one in the cost arithmetic or in the newline-anchored search cannot show. - No result may be evicted to pay for a wider invocation line, and under the fixture's uniform per-round costs the restored set must be the newest contiguous suffix. That second claim is a direction check: flipping the walk to oldest-first makes it a prefix and turns this red. The comment says so, and says plainly that contiguity is not guaranteed under mixed sizes, because the pass skips an unaffordable line with continue rather than break. - A checkpoint-covered call must keep its argument tail in the replayed suffix. Drop knownCallsOffset from the pass's callBefore bound and only this case notices, since that term is identically zero on the full-replay path. - A multi-byte argument must survive intact, with U+FFFD asserted absent so a failure names itself rather than only showing unequal strings. - The outputElided skip is load bearing, and finding that out took two tries. A sweep of single-result fixtures said the guard was dead code — elision appeared to always cut the invocation line too — and an adversarial counter-read found the configuration that sweep could not reach. Truncation alone cannot pay for a restoration: it undershoots its own budget by about 28 bytes. Initiator recovery can. With a ~519.7 KiB system prompt the equal-share pass cuts two trailing results to ~2.3 KiB, losing "output:" but keeping the clipped invocation line, and recovery then drops the older elided sibling to fit the user turn; those freed bytes become spare. The test searches that ~24-byte window rather than pinning a literal size, because pinning one made it pass on a two-character call id and fail on a twelve-character one, and it fails loudly if the window disappears. Each of the last three was verified by mutation. The two 600 KiB cap tests are byte-identical. The only src change is the comment recording what the guard actually depends on, and structure/providers/cursor.md records it too — the earlier draft of both called the guard defensive, which was wrong.
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Summary
Cursor root replay clipped a completed call's arguments even when almost the entire replay envelope
was unused.
CURSOR_INVOCATION_ARGUMENTS_BYTE_LIMIT(2 KiB) is charged insidetoolCallArgumentsTextwhile the envelope is still being built, so it cost a call 2 KiB whether ornot anything else wanted those bytes. A 4,693-byte successful
write_filelost its tail inside a6,011-byte replay of a 192-root / 512 KiB envelope, and because the replayed result text does not
repeat the argument, the model could no longer see what it had just written (#4516).
restoreClippedInvocationArgumentsadds a second pass inrootPromptMessages, afterselectedisassembled and before the roots are stored. It spends only leftover aggregate bytes
(
CURSOR_EXTERNAL_ROOT_BYTE_LIMITminus carried checkpoint bytes minus the assembled set), newesttoolResultroot first, skips a root whose own output was already elided, and never drops, shrinksor reorders a retained root.
clipped rather than evicting the output it describes. The two existing 600 KiB tests are unchanged
and still green; they are the proof the cap bites under pressure.
echoToolResultInRoot && replayedCalls, notexternalModel && replayedCalls. Nativecomposer-2.5echoes results into roots without being an external wire model(
isCursorExternalWireModelis false,cursorNeedsExternalToolContinuationis true), so thenarrower gate would have left the one native model that accumulates clipped invocation lines capped
for no reason.
String.prototype.replace, and its search is anchored on thepreceding newline. Serialized arguments routinely contain dollar-sign replacement patterns such as
$&,$'and$1, which the string form would expand into the surrounding match; andname:renders the result's tool name, which nothing sanitizes, so an unanchored search could be satisfied
by a crafted tool name and rewrite that header instead of the invocation.
The defect an adversarial counter-read found one layer down
pushDedupedbuilds a collapsed root's wire payload from the marked text but stored the unmarkedtext in the candidate's
textfield. Every consumer that rebuilds a root fromtextthereforedeleted the
[note: this exact output was produced N times in a row]line —truncateToolResultBlobalready did, and the new restoration pass did too. That note is therepetition breaker's per-entry half, so losing it re-primes the self-reinforcing loop the breaker
exists to end. The third commit stores the marked text, which makes
texta true mirror of thestored payload for the first time and fixes the truncation path by the same change. Its regression
test fails with that one line reverted and passes with it.
Coverage
Six tests added to
tests/providers/cursor/cursor-tool-result-invocation.test.ts: full restorationwhen the envelope is idle; a no-op below the cap; the native
composer-2.5path the gate exists for;verbatim handling of replacement patterns inside arguments; a 60-round 16 KiB fixture where the
aggregate lands at 511,484 of 524,288 bytes so the pass restores the newest 26 results and leaves 34
clipped, a hard stop at the envelope rather than an overrun; and the collapsed-repeat-run case above.
The fourth commit is a comment only. The two 600 KiB cap tests survive the refund because restoring a
600 KiB argument costs more than the whole envelope, so
cost > spareis always true there. That is asize-dependent skip rather than a rule that the line stays clipped, and shrinking those fixtures would
silently convert them from tests of the cap into tests of the refund. The block now says so.
structure/providers/cursor.mdgains a "Cursor root replay budgets" section, per theAGENTS.mdobligation that changing an owned source area updates its structure document. No document in
structure/stated this contract before, so the change adds a section rather than editing one.The second commit is a one-line follow-up to a hosted-CI typecheck failure:
request.rawMessagesisreadonly OcxMessage[]and the new parameter was declared mutable, which strict typecheck rejectswith TS4104. The pass only reads the array, so the parameter was widened rather than the array copied.
This claims nothing about #3506 causation. The four rejected patches in that issue were 1,648, 1,396,
1,670 and 1,900 bytes of serialized arguments, all under the 2 KiB cap, so none of them was clipped by
this code path and none of them is explained by this fix.
Verification
bun run typecheck, build andbun installwere NOT RUN. This branch wasdeveloped under an explicit instruction not to run them, so no local gate is offered as evidence for
this change.
tscwas invoked only to locate the TS4104 error hosted CI had already reported, whichis debugging rather than evidence.
run 34776361364 at
3d41c8c2d86e2d00276b89de22d4523478b9e89e, queued by the push itself on thepull_requestevent.An earlier explicit
workflow_dispatchon the same SHA was a duplicate of that run and wascancelled; a push to a branch with an open PR already queues a full run here, so the explicit
dispatch is only needed when a rebase or base sync leaves the head with no run of its own.
bun testruns undertests/providers/cursor/were used for debugging only and are notcited as proof of this change.
bun run structure:checkpasses, which is the gate that binds thestructure/document update.Checklist
Closes #4516