fix(git): replace mutating Stream.runFold with Stream.runForEach

[stephanschielke]

Issue for this PR

Closes #25873
Related: #25835

Type of change

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

What does this PR do?

Two fixes:

1. packages/opencode/src/git/index.ts -- replaces Stream.runFold with mutable accumulator with Stream.runForEach + local variables (original change in this PR).

2. packages/opencode/src/snapshot/index.ts (new commit) -- replaces Stream.mkUint8Array(handle.stdout) with an explicit Stream.runForEach + local variable collector. This is the actual crash site.

Root cause (fully confirmed)

TL;DR: effect@4.0.0-beta.59 changed Stream.mkUint8Array to use a mutable Channel.runFold accumulator. In Bun --compile --minify binaries, JSC freezes objects repeatedly passed to a loop step callback as a deoptimization guard. The second fold iteration receives a frozen accumulator and throws.

Full chain:

1. effect@4.0.0-beta.59 (bumped in fix(vcs): avoid unbounded diff memory usage #25581) changed Stream.mkUint8Array from returning a new Uint8Array on each iteration to mutating a shared { bytes, arrays } accumulator inside Channel.runFold.

2. snapshot/index.ts line 577 calls Stream.mkUint8Array(handle.stdout) to collect output from git cat-file --batch.

3. processor.ts calls snapshot.track() at case "start-step" -- after the first tool call completes and before the second starts.

4. Result: the second tool call in any session causes snapshot.track() to run git cat-file --batch, which calls Stream.mkUint8Array, which on the second chunk throws Attempted to assign to readonly property / Attempting to define property on object that is not extensible.

Why it appeared "git-specific": The original failing session had 35 tool calls in Step 1 (no snapshot needed yet), then git commands in Step 2. snapshot.track() fires at the step boundary, so the first git call in Step 2 triggered it. With fewer tools per step, the crash appears on call #2 regardless of tool type -- confirmed in Round 3 testing where a task tool call (no git, no subprocess) crashed as the second call.

Why bun run does not reproduce: JSC interprets object shapes differently when compiling with --minify. The freeze behavior is a JSC compiled-mode optimization, not present in interpreted mode.

Evidence:

• Effect diff 4.0.0-beta.57..4.0.0-beta.59 shows exactly one change to Stream.mkUint8Array -- switching from immutable to mutable accumulator.
• opencode.db confirms all 4 original errors are state.status = "error" with the tool input fully parsed (secureJsonParse succeeded) -- ruling out AI SDK JSON parsing as the throw site.
• Round 3 testing with local-anthropic agent on broken binary: call feat: compact and other improvements #1 (bash: echo hello world) succeeded, call Roadmap & Existing Issues #2 (task tool) failed.
• Upstream Effect issue filed: Stream.mkUint8Array crashes in Bun compiled+minified binaries: mutable Channel.runFold accumulator Effect-TS/effect-smol#2126
• Upstream Effect fix PR: fix(Stream): avoid mutable Channel.runFold accumulator in mkUint8Array Effect-TS/effect-smol#2127

Why the original git/index.ts fix was correct but incomplete

The git/index.ts Stream.runFold fix in the original commit is correct -- that mutable accumulator was also broken. But git/index.ts is only reached after execute() is called, which happens after snapshot.track() already crashed. So both fixes are needed.

How to reproduce

1. Build opencode with bun run build --single (compiled + minified)
2. Start with opencode serve
3. Use the local-anthropic agent (LM Studio Anthropic API) to trigger two consecutive tool calls
4. Second tool call fails with Attempted to assign to readonly property / Attempting to define property on object that is not extensible

Does NOT reproduce:

• With bun run (interpreted mode)
• With compiled but non-minified binary (bun build --compile without --minify)
• With effect 4.0.0-beta.57 (last good version)
• With effect 4.0.0-beta.60 (does NOT fix Stream.mkUint8Array)

How did you verify your code works?

1. Confirmed root cause via Effect repo git diff (beta.57..beta.59, 255 lines, only change to Stream.mkUint8Array in Stream.ts).
2. Verified via SQLite DB queries: all error tool calls have fully parsed input (secureJsonParse succeeded, throw site is post-parse).
3. Round 3 reproduction: local-anthropic agent on broken binary reproduces on demand -- call Roadmap & Existing Issues #2 fails regardless of tool type.
4. packages/opencode/src/snapshot/index.ts LSP diagnostics: clean after fix.
5. No other Stream.mkUint8Array calls in the codebase (confirmed via grep).

Checklist

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

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