fix(shared): bound the file-link label so bracket runs stop rescanning

[tsouth89]

fix(shared): bound the file-link label so bracket runs stop rescanning

What changed

FILE_LINK_TOKEN_REGEX in packages/shared/src/composerInlineTokens.ts let the
label body repeat without a bound:

/(^|\s)\[((?:\\.|[^\]\\])*)\]\(([^)\s]+)\)(?=\s)/g

This caps it at 512 characters. Two files, +36/-1.

Why it should exist

With an unbounded body, every whitespace in the composer is a candidate start:
the engine scans the rest of the text for a closing ], fails, then rescans
from the next whitespace. On a run of unterminated brackets that is quadratic,
and collectComposerInlineTokens runs on raw composer text — so pasting one
freezes the tab.

Measured on " [[" repeated, before → after:

input	before	after
30k chars	167ms	8ms
60k chars	676ms	17ms
120k chars	2838ms	33ms

Doubling the input quadruples the old time, which is the quadratic signature.

Scope, stated honestly: ordinary pastes are unaffected, because a ] anywhere
ahead bounds each attempt. A 104k-char markdown table of [a] [b] [c] cells and
a 172k-char code paste full of arr[i][j][k] both measure 0ms before and after.
The trigger is a long run of [ with no closing bracket following. So this is a
self-inflicted UI freeze on degenerate or hostile paste content, not a server-side
availability issue — worth fixing, not worth alarm.

Why the cap is safe

The cap cannot reject a link anyone could meaningfully write. Only a basename
survives the label !== basename check immediately below the match, and the
longest filename any common filesystem allows is 255.

How it was verified

Behavioural equivalence against the old pattern over 156,504 generated
inputs — exhaustive triples over an alphabet of [ ] ( ) \ @ ", tab, newline,
space and path-ish fragments; structured [label](path) shapes across prefix and
suffix contexts; and 150,000 randomized fuzz strings. Compared match count, match
offsets, and every capture group.

Zero differences.

The single intended difference is at the cap itself: a 512-character label still
matches, 513 no longer does. The two new boundary tests pin exactly that, and a
third asserts the bracket-run case completes in under a second.

No UI change, so no screenshots — this is pure tokenizer logic behind the
composer.

---

Note

Low Risk
Localized tokenizer regex change with extensive equivalence testing; only rejects implausibly long link labels and improves client-side paste performance.

Overview
Fixes composer freezes when pasted text has long runs of unclosed [ brackets by capping how much of a [label](path) label the file-link regex will scan.

FILE_LINK_TOKEN_REGEX in composerInlineTokens.ts no longer uses an unbounded label repeat; it limits the label body to 512 characters via MAX_FILE_LINK_LABEL_LENGTH, so each match attempt is constant-bounded instead of rescanning the rest of the string from every whitespace (quadratic on inputs like repeated " [[").

Normal file links are unchanged in practice because only basenames pass validation and real filenames are far below the cap. Links with labels at 512 chars still tokenize; longer labels are left as plain text.

Tests add cap boundary cases and a performance guard on a 40k-char unterminated bracket run.

^{Reviewed by Cursor Bugbot for commit 9b71e34. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Bound file-link label length to 512 chars to prevent catastrophic bracket rescanning

• Introduces MAX_FILE_LINK_LABEL_LENGTH = 512 in composerInlineTokens.ts and rebuilds FILE_LINK_TOKEN_REGEX with a bounded quantifier to cap label body length.
• Prevents catastrophic backtracking when the tokenizer encounters long runs of unterminated brackets.
• Behavioral Change: file link tokens with labels exceeding 512 characters are no longer recognized.

^{Macroscope summarized 9b71e34.}

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[macroscopeapp]

Approvability

Verdict: Approved 9b71e34

This is a straightforward performance bug fix that bounds a regex to prevent quadratic backtracking on pathological input. The 512-character limit is generous (max filename is 255) and includes comprehensive tests verifying the boundary behavior.

^{You can customize Macroscope's approvability policy. Learn more.}