Add tests for writeMarkerSection in sync-team.ts to cover marker-replacement edge cases

[sebastianbarrozo]

Summary

tools/sync-team.ts has zero test coverage. The most critical gap is writeMarkerSection, which mutates CLAUDE.md and opencode.md by finding <!-- FYSO TEAM START --> / <!-- FYSO TEAM END --> markers and replacing the content between them. Its string-index logic has untested edge cases that could silently corrupt these configuration files during team sync.

Evidence

• File: opencode-plugin/src/tools/sync-team.ts, function writeMarkerSection (lines ~40-58).
• Bug scenario 1 — partial markers: If the file contains <!-- FYSO TEAM START --> but not <!-- FYSO TEAM END --> (e.g., user edited the file and accidentally deleted the closing marker), the function falls through to appending a second full section instead of reporting or recovering. Repeated syncs would keep appending duplicates.
• Bug scenario 2 — multiple marker pairs: If the file has two START/END pairs (e.g., from a prior duplication bug), indexOf finds the first START and first END, potentially slicing across unrelated content.
• Impact: These files drive agent behavior configuration. Corruption goes undetected until the user notices broken prompts.

Acceptance criteria

• Unit tests for writeMarkerSection covering: fresh file (no markers), existing file with valid markers (replace), file with START but no END, file with END but no START, file with multiple marker pairs.
• Unit tests for getColor and firstLineOf utility functions.
• Tests use a temp directory (no real filesystem side effects).
• All tests pass in CI.

Suggested validation

Create opencode-plugin/src/tools/sync-team.test.ts. The partial-marker tests should fail before any fix to writeMarkerSection is applied (confirming the edge case exists) and pass after the fix. Run with npx vitest run src/tools/sync-team.test.ts.

Pipeline

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