perf: fast lexer using charCodeAt comparisons and sticky regexes

[Copilot]

Applies the es-module-shims fast lexer principles to the CSS parser: numeric character-code comparisons instead of string comparisons, and sticky regexes to eliminate substring allocations.

Lexer (src/parse/lexer.ts)

• charCodeAt() over string indexing — all hot-path character checks (skipWhitespace, tryOpenBrace, tryCloseBrace, tryColon, skipSemicolonAndWhitespace, tryCommaAndWhitespace) now compare numeric char codes against named constants instead of creating single-char strings
• Sticky regex matching — matchRegex() sets re.lastIndex = this.pos and matches against the full input with the y flag, eliminating the this.remaining substring slice (previously O(n) allocation per call)
• Range-based advance — _advanceRange(from, to) iterates the original input by index instead of receiving an intermediate string

// Before: string comparison + substring allocation
const ch = this.input[this.pos];        // allocates 1-char string
if (ch === '{') { ... }
const m = re.exec(this.remaining);      // allocates O(n) substring

// After: numeric comparison + sticky regex on full input
const ch = this.input.charCodeAt(this.pos);  // returns number
if (ch === Ch_OPEN) { ... }
re.lastIndex = this.pos;
const m = re.exec(this.input);               // no allocation

Parser (src/parse/index.ts)

• Pre-compiled sticky regexes at module scope — all 20+ regex patterns (re_comment, re_media, re_keyframesName, re_pageMarginBox, etc.) compiled once as y-flag constants instead of per-parse() call
• Inlined at-rule parsers — replaced _compileAtRule factory with explicit functions using module-level regex constants for @import, @charset, @namespace
• charCodeAt guards — lexer.charAt() === '@' → lexer.charCodeAt() === Ch_AT throughout

String search utilities (src/utils/stringSearch.ts)

• charCodeAt() for character dispatch in bracket/quote-aware search loops

Security

9 CodeQL ReDoS alerts on @import/@charset/@namespace regex patterns are pre-existing — the pattern is unchanged from the original _compileAtRule factory, only moved to module scope. The at-import-dos test case validates handling of pathological input.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• guybedford.com
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)
• web.archive.org
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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