fix(tui,coding-agent): survive lone surrogates in table cells and terminate the WebP EXIF scan

[snimu]

Summary

Two rendering-input crashes:

• Lone UTF-16 surrogates no longer crash table rendering. Table cell selection markers encode cell content with encodeURIComponent, which throws URIError: URI malformed on a lone surrogate (e.g. text split mid-astral-character at a cell boundary) — taking down the whole TUI render. Content is now sanitized with toWellFormed() (available on every supported runtime, Node ≥ 20) so the surrogate becomes U+FFFD and the marker round-trips. Fixes the defect reported in discussion [Bug] TUI crashes with URIError in cellMarker when rendering markdown tables #2001.
• A corrupt or crafted WebP can no longer hang the process. The RIFF chunk scan read the 32-bit chunk size with signed arithmetic; a size with the high bit set went negative and walked the scan offset backward, spinning the EXIF-orientation scan forever on the main thread. Chunk sizes — and the little-endian TIFF read32, which had the same signedness bug — are now read unsigned, guaranteeing forward progress. Fixes the defect reported in discussion A malformed WebP chunk size hangs the agent forever: RIFF size decoded with a signed shift #1554.

Validation

• two pins, each verified fail-unfixed: a lone-surrogate cell round-trips (pre-fix: URIError), and a WebP whose chunk size re-visits its own offset terminates (pre-fix: infinite loop — the unfixed run had to be killed after 20s)
• packages/tui vitest include list gains the new selection-metadata suite (the package runs an explicit whitelist)
• root npm run check passes via the pre-commit hook

LOC

Total src: +6/−3 (net +3); tests: +35/−0 (net +35).
Src +7/−3 (both point fixes, no new mechanism). Tests +34, changelog 2 fragments, 1 vitest include line.

Linear: RES-1266 https://linear.app/primeintellect/issue/RES-1266

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Note

Low Risk
Targeted defensive fixes in rendering metadata and binary parsing; behavior only changes for previously crashing or hanging malformed inputs.

Overview
Fixes two input-handling failures in the TUI and image EXIF path.

Table selection markers no longer throw when cell content includes a lone UTF-16 surrogate. cellMarker runs content through toWellFormed() before encodeURIComponent, so malformed sequences become U+FFFD and markers still round-trip through extraction.

WebP EXIF orientation no longer hangs on corrupt or crafted files. Chunk sizes and little-endian TIFF read32 values are coerced with >>> 0 so high-bit sizes are not treated as negative offsets that move the RIFF scan backward in a loop; the scan exits and orientation falls back to default instead.

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Note

Fix WebP EXIF scan termination and lone-surrogate handling in TUI selection markers

• Forces unsigned 32-bit interpretation of RIFF chunk sizes and TIFF offsets in exif-orientation.ts, so a high-bit size no longer moves the scan backward and loops forever.
• Runs well-formed-string conversion before URI-encoding cell content in selection-metadata.ts, replacing lone UTF-16 surrogates with U+FFFD so encoding does not throw.
• Adds regression tests for both fixes in exif-orientation.test.ts and selection-metadata.test.ts.
• Risk: readOrientationFromTiff and findWebpTiffOffset now treat offsets/sizes with the high bit set as large unsigned values rather than negative; malformed inputs that previously errored early via negative-offset paths will instead be caught by existing bounds checks.

^{Macroscope summarized a3d1139.}

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