#20204: fix(sessions): allow negative IDs and colon separators in session IDs

## Summary Fixes #20158 Messages sent to Telegram forum topics in groups with negative chat IDs were being silently dropped because the session ID validation regex rejected them. ## Root Cause `SAFE_SESSION_ID_RE` (`/^[a-z0-9][a-z0-9._-]{0,127}$/i`) required session IDs to start with alphanumeric characters and didn't allow colons. This rejected: - Negative Telegram IDs: `-1003110470591` (starts with `-`) - Topic separators: `-1003110470591:91088` (contains `:`) ## Changes - Allow session IDs to start with `-` for negative Telegram group/channel IDs - Allow `:` in session IDs for forum topic ID separators - Added test coverage --- 🤖 Generated with Claude Code <!-- greptile_comment --> <h3>Greptile Summary</h3> This PR fixes session ID validation to support Telegram forum topics in groups with negative chat IDs. The `SAFE_SESSION_ID_RE` regex is updated from `/^[a-z0-9][a-z0-9._-]{0,127}$/i` to `/^-?[a-z0-9][a-z0-9._:-]{0,127}$/i`, allowing an optional leading `-` and `:` as a separator character. - **`src/config/sessions/paths.ts`**: Regex updated to accept negative Telegram group IDs (e.g., `-1003110470591`) and colon-separated forum topic IDs (e.g., `-1003110470591:91088`). The change is safe — neither `-` nor `:` enables path traversal, and `resolvePathWithinSessionsDir` provides an additional containment check. - **`src/config/sessions/sessions.test.ts`**: Adds test coverage for the two new accepted formats. - No issues found. The fix is minimal, well-scoped, and addresses a real bug where Telegram forum topic messages were silently dropped. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge — it's a minimal, well-scoped regex fix with no security or path traversal risk. - The change is a two-character addition to a regex character class plus an optional leading dash. Neither `-` nor `:` enables path traversal, and the downstream path resolution function provides additional containment. The fix addresses a real bug (Telegram forum topic messages being silently dropped) with appropriate test coverage. No issues found. - No files require special attention. _{Last reviewed commit: 4179f43} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->