Issue for this PR

Closes #17047

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Tool.define() wraps toolInfo.execute with a validation + truncation layer each time init() is called. When init is an object literal (not a function), line 55 returns the same object reference every call. This means each init() call:

1. Captures the current toolInfo.execute (already wrapped N times)
2. Overwrites it with wrapper N+1 that calls the previous one
3. Builds a closure chain: wrap_N → wrap_{N-1} → ... → wrap_1 → original

This is an unbounded memory leak — each wrapper closure (~1KB) is retained permanently and can never be GC'd. At production traffic (~800 sessions/hr, ~10 steps/session), this leaks ~8MB/hr.

After ~1,000+ accumulated steps, invoking any affected tool recurses through the entire chain and crashes with RangeError: Maximum call stack size exceeded.

Affected tools: all object-defined tools (Read, Glob, Grep, Edit, Write, TodoRead, TodoWrite). Function-defined tools (Bash, Task, WebSearch, etc.) are safe because await init(initCtx) returns a fresh object each time.

The fix: shallow-copy the object with { ...init } so each init() call gets a fresh copy. The original object is never mutated, each copy gets exactly one wrapper layer, and the copy is GC'd after the step completes. This matches how function-defined tools already work.

How did you verify your code works?

1. Regression tests (test/tool/tool-define.test.ts) — 5 tests that directly verify the fix:

Tests 1 and 4 fail without the fix, confirming they catch the exact bug.

2. Stress testing — ran opencode serve under sustained load (~5,000 sessions/hr, 128 concurrent workers). Without the fix, RangeErrors started appearing at ~1,275 sessions. Stack trace confirmed tool.ts:69 repeated hundreds of times. With the fix applied, no RangeErrors after thousands of sessions.

3. Typecheck — bun turbo typecheck passes (all 13 packages).

Screenshots / recordings

Stack trace captured from a failing instance (pre-fix), showing tool.ts:69 recursion:

RangeError: Maximum call stack size exceeded.
    at containsPath (src/project/instance.ts:97:29)
    at assertExternalDirectory (src/tool/external-directory.ts:17:16)
    at execute (src/tool/read.ts:45:11)
    at <anonymous> (src/tool/tool.ts:69:32)
    at <anonymous> (src/tool/tool.ts:69:32)
    at <anonymous> (src/tool/tool.ts:69:32)
    [... repeated hundreds of times ...]

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR