fix(acp): use truncateUtf16Safe for event mapper error text truncation by lsr911 · Pull Request #101535 · openclaw/openclaw

lsr911 · 2026-07-07T09:35:53Z

What Problem This Solves

ACP event mapper truncates error argument values with .slice(0, 100). Tool call arguments and error text may contain CJK characters or emoji — a slice boundary in the middle of a surrogate pair produces U+FFFD in operator-visible warning messages.

Why This Change Was Made

Replace .slice(0, 100) with truncateUtf16Safe().

Evidence

- const safe = raw.length > 100 ? `${raw.slice(0, 100)}...` : raw;
+ const safe = raw.length > 100 ? `${truncateUtf16Safe(raw, 100)}...` : raw;

Part of the UTF-16 safety sweep.

Issue

N/A

🤖 Generated with Claude Code

.slice(0, 100) on ACP event argument values can split surrogate pairs from emoji or CJK text, producing U+FFFD in error/warning notices shown to operators. Co-Authored-By: Claude <[email protected]>

clawsweeper · 2026-07-07T09:48:59Z

Codex review: needs real behavior proof before merge. Reviewed July 7, 2026, 6:44 AM ET / 10:44 UTC.

Summary
The PR replaces ACP tool-title truncation in src/acp/event-mapper.ts with truncateUtf16Safe and adds a formatToolTitle surrogate-pair regression test.

PR surface: Source +1, Tests +10. Total +11 across 2 files.

Reproducibility: yes. Current main and v2026.6.11 use raw.slice(0, 100) in the ACP title formatter, and a focused Node probe shows that boundary can leave a dangling high surrogate that renders as a replacement character.

Review metrics: none identified.

Merge readiness
Overall: 🧂 unranked krab
Proof: 🧂 unranked krab
Patch quality: 🦞 diamond lobster
Result: blocked until real behavior proof is added.

Overall follows the weaker of proof and patch quality, so missing proof can cap an otherwise strong patch.

Rank-up moves:

[P1] Add redacted real ACP output, terminal screenshot, log, or recording showing a boundary-case emoji/CJK tool argument truncates without a replacement character.

Proof guidance:

[P1] Needs real behavior proof before merge: Missing: add redacted terminal/live ACP output, a terminal screenshot, logs, recording, or artifact showing the fixed title path, then update the PR body to trigger re-review.

Risk before merge

[P1] After-fix ACP runtime proof is still absent; the new unit test and green checks do not substitute for real operator-visible ACP output.

Maintainer options:

Decide the mitigation before merge
Land the narrow helper swap with the focused regression test after the PR body includes redacted real ACP output showing boundary-case tool titles no longer contain replacement characters.
Pause or close
Do not merge this PR until maintainers decide whether the risk is worth taking.

Next step before merge

[P1] No repair lane is appropriate because the remaining blocker is contributor-supplied real ACP behavior proof, not a narrow code defect for ClawSweeper to fix.

Security
Cleared: The diff only calls an existing local string truncation helper and adds a focused test; it does not change dependencies, workflows, permissions, secrets, or code execution paths.

Review details

Best possible solution:

Land the narrow helper swap with the focused regression test after the PR body includes redacted real ACP output showing boundary-case tool titles no longer contain replacement characters.

Do we have a high-confidence way to reproduce the issue?

Yes. Current main and v2026.6.11 use raw.slice(0, 100) in the ACP title formatter, and a focused Node probe shows that boundary can leave a dangling high surrogate that renders as a replacement character.

Is this the best way to solve the issue?

Yes. Reusing the existing surrogate-safe helper at the exact title truncation point is the narrowest maintainable fix; the remaining gap is real ACP behavior proof, not code shape.

AGENTS.md: found and applied where relevant.

Codex review notes: model internal, reasoning high; reviewed against 942b44966107.

Label changes

Label justifications:

P2: This is a normal limited-blast-radius ACP display bug fix for corrupted operator-visible tool-title text.
rating: 🧂 unranked krab: Overall readiness is 🧂 unranked krab; proof is 🧂 unranked krab and patch quality is 🦞 diamond lobster.
status: 📣 needs proof: The PR needs real behavior proof before ClawSweeper can clear the contributor ask. Needs real behavior proof before merge: Missing: add redacted terminal/live ACP output, a terminal screenshot, logs, recording, or artifact showing the fixed title path, then update the PR body to trigger re-review.

Evidence reviewed

PR surface:

Source +1, Tests +10. Total +11 across 2 files.

View PR surface stats

Area	Files	Added	Removed	Net
Source	1	2	1	+1
Tests	1	11	1	+10
Docs	0	0	0	0
Config	0	0	0	0
Generated	0	0	0	0
Other	0	0	0	0
Total	2	13	2	+11

What I checked:

Current main still has the bug: Current main formats ACP tool titles with raw.slice(0, 100), so a surrogate pair can still be split before this PR lands. (src/acp/event-mapper.ts:312, 942b44966107)
Latest release still has the bug: The latest release v2026.6.11 also uses raw.slice(0, 100) in the same ACP title path, so the fix is not shipped. (src/acp/event-mapper.ts:311, e085fa1a3ffd)
PR head applies the narrow helper swap: The PR head imports truncateUtf16Safe and replaces only the unsafe title truncation call in formatToolTitle. (src/acp/event-mapper.ts:313, 743956dfd270)
PR head adds focused regression coverage: The new test covers the boundary case of 99 ASCII characters followed by an emoji, expecting the dangling surrogate to be dropped before appending the truncation marker. (src/acp/event-mapper.test.ts:22, 743956dfd270)
Helper contract is appropriate: truncateUtf16Safe delegates to sliceUtf16Safe, which removes dangling surrogate halves at the truncation boundary. (packages/normalization-core/src/utf16-slice.ts:43, 942b44966107)
ACP caller path emits the title: The ACP translator passes tool-event args through formatToolTitle and emits the resulting title in a tool_call session update. (src/acp/translator.ts:892, 942b44966107)

Likely related people:

steipete: GitHub commit history shows Peter Steinberger authored the original experimental ACP support and later normalization-core extraction that provides truncateUtf16Safe; he also added the second commit with the focused regression test on this PR. (role: feature owner and recent area contributor; confidence: high; commits: de3b68740aa9, 062f88e3e3af, 743956dfd270; files: src/acp/event-mapper.ts, src/acp/translator.ts, packages/normalization-core/src/utf16-slice.ts)
jacobtomlinson: Commit 464e2c1 added ACP terminal tool-title sanitization in the same mapper/client-test surface, making this closely related to the current title-formatting behavior. (role: adjacent ACP title hardening contributor; confidence: medium; commits: 464e2c10a5ed; files: src/acp/event-mapper.ts, src/acp/client.test.ts)
Bartok9: PR history shows Bartok9 authored the related tool-display UTF-16 truncation fix that established the same helper pattern for avoiding replacement characters at display boundaries. (role: adjacent UTF-16 truncation fix author; confidence: medium; commits: e09b9dfc1ba9; files: src/utils.ts, packages/normalization-core/src/utf16-slice.ts)

What the crustacean ranks mean

🦀 challenger crab: rare, exceptional readiness with strong proof, clean implementation, and convincing validation.
🦞 diamond lobster: very strong readiness with only minor maintainer review expected.
🐚 platinum hermit: good normal PR, likely mergeable with ordinary maintainer review.
🦐 gold shrimp: useful signal, but proof or patch confidence is still limited.
🦪 silver shellfish: thin signal; proof, validation, or implementation needs work.
🧂 unranked krab: not merge-ready because proof is missing/unusable or there are serious correctness or safety concerns.
🌊 off-meta tidepool: rating does not apply to this item.

Shiny media proof means a screenshot, video, or linked artifact directly shows the changed behavior. Runtime, network, CSP, and security claims still need visible diagnostics.

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Review history (1 earlier review cycle)

reviewed 2026-07-07T09:54:23.561Z sha f6a5dab :: needs real behavior proof before merge. :: none

steipete · 2026-07-07T11:10:11Z

Land-ready at exact head 8fbcf4f4620125eaa7fa7bc2e8ee776141724803.

Maintainer review improved the dependency boundary by replacing the broad normalization package import with the leaf @openclaw/normalization-core/utf16-slice entry point. The caller-level regression covers formatToolTitle at the 100-code-unit preview boundary and verifies a supplementary character is never split.

Validation:

canonical formatting and git diff --check
fresh Codex autoreview: clean, correctness confidence 0.92
exact-head hosted CI: 72 passing checks, no failures or pending checks
scripts/pr review-validate-artifacts 101535
OPENCLAW_TESTBOX=1 scripts/pr prepare-run 101535

No known proof gaps.

steipete · 2026-07-07T11:10:33Z

Merged via squash.

Prepared head SHA: 8fbcf4f4620125eaa7fa7bc2e8ee776141724803
Landed commit: 42fc9e8a92f992c82a06ea52d125cffc7cd19c6f

openclaw#101535) * fix(acp): use truncateUtf16Safe for event mapper error text truncation .slice(0, 100) on ACP event argument values can split surrogate pairs from emoji or CJK text, producing U+FFFD in error/warning notices shown to operators. Co-Authored-By: Claude <[email protected]> * test(acp): cover UTF-16-safe tool titles * refactor(acp): keep event mapper import leaf-only --------- Co-authored-by: Claude <[email protected]> Co-authored-by: Peter Steinberger <[email protected]>

fix(acp): use truncateUtf16Safe for event mapper error text truncation

f6a5dab

.slice(0, 100) on ACP event argument values can split surrogate pairs from emoji or CJK text, producing U+FFFD in error/warning notices shown to operators. Co-Authored-By: Claude <[email protected]>

openclaw-barnacle Bot added the size: XS label Jul 7, 2026

steipete added 2 commits July 7, 2026 11:23

test(acp): cover UTF-16-safe tool titles

743956d

refactor(acp): keep event mapper import leaf-only

8fbcf4f

steipete merged commit 42fc9e8 into openclaw:main Jul 7, 2026
101 checks passed

This was referenced Jul 7, 2026

fix(agents): keep tool/command display truncation UTF-16 safe #101613

Closed

fix(cli): keep CLI display/approval truncation UTF-16 safe #101633

Closed

github-actions Bot mentioned this pull request Jul 7, 2026

📡 Upstream Digest — 2026-07-07 14:10 UTC curtismercier/openclaw-mods#1230

Open

lsr911 mentioned this pull request Jul 9, 2026

fix(tool-policy-audit): use truncateUtf16Safe for audit field truncation #102464

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fix(acp): use truncateUtf16Safe for event mapper error text truncation#101535

fix(acp): use truncateUtf16Safe for event mapper error text truncation#101535
steipete merged 3 commits into
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lsr911:fix/utf16-safe-event-mapper

lsr911 commented Jul 7, 2026

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lsr911 commented Jul 7, 2026

What Problem This Solves

Why This Change Was Made

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