fix: replace unsupported lookahead regex in create-github-release.rs

[konard]

Summary

Fixes #137 — GitHub release for v0.3.0 failed because scripts/create-github-release.rs used a regex lookahead assertion (?=...) which is not supported by Rust's regex crate.

Root Cause

The get_changelog_for_version function at line 46 used:

let pattern = format!(r"(?s)## \[{}\].*?\n(.*?)(?=\n## \[|$)", escaped_version);
let re = Regex::new(&pattern).unwrap();  // panics at runtime!

The regex crate does not support look-around (lookahead/lookbehind) by design — it guarantees linear-time matching using finite-state automata, which is incompatible with backtracking required by lookaheads. The script panicked at runtime with:

regex parse error: (?s)## \[0\.3\.0\].*?\n(.*?)(?=\n## \[|$)
error: look-around, including look-ahead and look-behind, is not supported
Process completed with exit code 101.

As a result, the v0.3.0 Git tag was created and the crate was published to crates.io, but the GitHub release was never created — leaving versions out of sync.

Fix

Replace the lookahead with a non-capturing group:

// Use a pattern without lookahead (not supported by the `regex` crate).
// Match the section header and capture everything until the next section or end of string.
let pattern = format!(r"(?s)## \[{}\][^\n]*\n(.*?)(?:\n## \[|$)", escaped_version);

Key changes:

• (?=\n## \[|$) (lookahead, unsupported) → (?:\n## \[|$) (non-capturing group, supported)
• .*? after version header → [^\n]* (more precisely matches the rest of the header line)

Verified by experiment script experiments/test-changelog-regex.rs — all three cases pass:

• Extracts correct section for a given version ✓
• Does not bleed into adjacent sections ✓
• Falls back to "Release v{version}" when version not found ✓

Workaround Applied

Since the v0.3.0 tag and crates.io publication already succeeded, the GitHub release was manually created as a workaround: https://github.com/linksplatform/Numbers/releases/tag/v0.3.0

Case Study

Full root cause analysis, timeline, and possible solutions are documented in docs/case-studies/issue-137/README.md.

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