feat: unify chat sin_edit with MCP surgical editor and add sin_replace (issue #373)

[Delqhi]

Summary

Aligns the chat tool sin_edit with the MCP surgical editor by routing it through the shared internal edit engine. Preserves the previous naive string-replace behavior as a new sin_replace tool for backward compatibility.

Changes

• Added exported internal.EditByString(path, old, new) helper in cmd/sin-code/internal/edit.go.
• Refactored toolEdit in cmd/sin-code/chat_tools.go to call internal.EditByString.
• Added sin_replace chat tool that retains the old naive strings.Replace behavior.
• Added sin_replace to builtinSpecs and builtinTool dispatch.
• Added sin_replace permission default (allow) in cmd/sin-code/internal/permission_defaults.go.
• Added unit tests for the new sin_edit ambiguity behavior and sin_replace first-occurrence replacement.

Verification

• go build ./cmd/sin-code/... passes.
• Targeted race tests pass:
  • go test ./cmd/sin-code -run 'TestArgBool|TestTool|TestMaybeGenerateTest|TestChat|TestMCP' -race -count=1
  • go test ./cmd/sin-code/internal -run 'TestEdit|TestString|TestApply|TestPermission|TestServeIntegration' -race -count=1
• The full go test ./cmd/sin-code/... -race -count=1 run has unrelated pre-existing failures (autonomy build error, golden help mismatch, EFM Docker/OrbStack environment issues, agentloop concurrency timing flake) that are not introduced by this change.

Closes #373

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Project	Deployment	Actions	Updated (UTC)
sin-code	Ready	Preview, Comment, Open in v0	Jun 18, 2026 9:08pm

[github-actions]

🏆 CEO Audit — A+ (100.0/100)

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[github-actions]

🏆 CEO Audit — A+ (100.0/100)

Metric	Value
Grade	A+
Score	100.0/100
Critical findings	0
High findings	0
Medium findings	0
Profile	QUICK
Min grade gate	B

📥 Download full report (Markdown)

Run ID: 27789433720 · Commit: ${github.sha}

Run ~/.config/opencode/skills/ceo-audit/scripts/audit.sh . --profile=QUICK locally to reproduce.