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fix (git): Truncate oversized git output for commit generation #1275

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fix (git): Truncate oversized git output for commit generation #1275

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18 changes: 12 additions & 6 deletions apps/server/src/git/Layers/GitCore.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,8 @@ interface ExecuteGitOptions {
timeoutMs?: number | undefined;
allowNonZeroExit?: boolean | undefined;
fallbackErrorMessage?: string | undefined;
maxOutputBytes?: number | undefined;
truncateOutput?: boolean | undefined;
}

function parseBranchAb(value: string): { ahead: number; behind: number } {
Expand Down Expand Up @@ -237,6 +239,8 @@ const makeGitCore = Effect.gen(function* () {
args,
allowNonZeroExit: true,
...(options.timeoutMs !== undefined ? { timeoutMs: options.timeoutMs } : {}),
...(options.maxOutputBytes !== undefined ? { maxOutputBytes: options.maxOutputBytes } : {}),
...(options.truncateOutput !== undefined ? { truncateOutput: options.truncateOutput } : {}),
})
.pipe(
Effect.flatMap((result) => {
Expand Down Expand Up @@ -793,12 +797,14 @@ const makeGitCore = Effect.gen(function* () {
return null;
}

const stagedPatch = yield* runGitStdout("GitCore.prepareCommitContext.stagedPatch", cwd, [
"diff",
"--cached",
"--patch",
"--minimal",
]);
const stagedPatch = yield* executeGit(
"GitCore.prepareCommitContext.stagedPatch",
cwd,
["diff", "--cached", "--patch", "--minimal"],
{
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Copilot AI Mar 21, 2026

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For prepareCommitContext the staged patch is later truncated to 50,000 chars in GitManager.limitContext(...), but this git diff --cached --patch call still captures up to the GitService default maxOutputBytes (1,000,000). Consider passing an explicit smaller maxOutputBytes here (plus a small buffer) to avoid unnecessary read/decoding work on large diffs and to make the intended cap explicit at this call site.

Suggested change
{
{
// Limit output to slightly above the 50,000-character context cap used later.
maxOutputBytes: 60_000,

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truncateOutput: true,
},
).pipe(Effect.map((result) => result.stdout));

return {
stagedSummary,
Expand Down
34 changes: 34 additions & 0 deletions apps/server/src/git/Layers/GitManager.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -729,6 +729,40 @@ it.layer(GitManagerTestLayer)("GitManager", (it) => {
}),
);

it.effect("creates a commit when the staged patch exceeds the capture limit", () =>
Effect.gen(function* () {
const repoDir = yield* makeTempDir("t3code-git-manager-");
yield* initRepo(repoDir);
fs.writeFileSync(path.join(repoDir, "huge.txt"), "line\n".repeat(250_000));
let generatedPatchLength = 0;

const { manager } = yield* makeManager({
textGeneration: {
generateCommitMessage: (input) =>
Effect.sync(() => {
generatedPatchLength = input.stagedPatch.length;
return {
subject: "Commit huge patch",
body: "",
};
}),
},
});
const result = yield* runStackedAction(manager, {
cwd: repoDir,
action: "commit",
});

expect(result.commit.status).toBe("created");
expect(generatedPatchLength).toBe(50_013);
expect(
yield* runGit(repoDir, ["log", "-1", "--pretty=%s"]).pipe(
Effect.map((gitResult) => gitResult.stdout.trim()),
),
).toBe("Commit huge patch");
}),
);

it.effect("uses custom commit message when provided", () =>
Effect.gen(function* () {
const repoDir = yield* makeTempDir("t3code-git-manager-");
Expand Down
17 changes: 17 additions & 0 deletions apps/server/src/git/Layers/GitService.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,23 @@ layer("GitServiceLive", (it) => {
}),
);

it.effect("runGit can truncate oversized output when requested", () =>
Effect.gen(function* () {
const gitService = yield* GitService;
const result = yield* gitService.execute({
operation: "GitProcess.test.truncateOutput",
cwd: process.cwd(),
args: ["--version", "--build-options"],
maxOutputBytes: 16,
truncateOutput: true,
});

assert.equal(result.code, 0);
assert.ok(result.stdout.length <= 16);
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Copilot AI Mar 21, 2026

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This test asserts result.stdout.length <= 16, but maxOutputBytes is a byte limit while .length is a UTF-16 code unit count. To make the test accurately reflect the contract (and avoid edge cases if output ever contains non-ASCII), assert against Buffer.byteLength(result.stdout, 'utf8') (or similar) instead of string length.

Suggested change
assert.ok(result.stdout.length <= 16);
assert.ok(Buffer.byteLength(result.stdout, "utf8") <= 16);

Copilot uses AI. Check for mistakes.
assert.equal(result.stdoutTruncated, true);
}),
);

it.effect("runGit fails with GitCommandError when non-zero exits are not allowed", () =>
Effect.gen(function* () {
const gitService = yield* GitService;
Expand Down
44 changes: 36 additions & 8 deletions apps/server/src/git/Layers/GitService.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,11 @@ import {
const DEFAULT_TIMEOUT_MS = 30_000;
const DEFAULT_MAX_OUTPUT_BYTES = 1_000_000;

interface CollectedOutput {
text: string;
truncated: boolean;
}

function quoteGitCommand(args: ReadonlyArray<string>): string {
return `git ${args.join(" ")}`;
}
Expand All @@ -43,28 +48,44 @@ const collectOutput = Effect.fn(function* <E>(
input: Pick<ExecuteGitInput, "operation" | "cwd" | "args">,
stream: Stream.Stream<Uint8Array, E>,
maxOutputBytes: number,
): Effect.fn.Return<string, GitCommandError> {
truncateOutput: boolean,
): Effect.fn.Return<CollectedOutput, GitCommandError> {
const decoder = new TextDecoder();
let bytes = 0;
let text = "";
let truncated = false;

yield* Stream.runForEach(stream, (chunk) =>
Effect.gen(function* () {
bytes += chunk.byteLength;
if (bytes > maxOutputBytes) {
if (truncated) {
return;
}

const nextBytes = bytes + chunk.byteLength;
if (nextBytes > maxOutputBytes) {
if (truncateOutput) {
const remainingBytes = maxOutputBytes - bytes;
if (remainingBytes > 0) {
text += decoder.decode(chunk.subarray(0, remainingBytes), { stream: true });
bytes = maxOutputBytes;
}
truncated = true;
return;
}
return yield* new GitCommandError({
operation: input.operation,
command: quoteGitCommand(input.args),
cwd: input.cwd,
detail: `${quoteGitCommand(input.args)} output exceeded ${maxOutputBytes} bytes and was truncated.`,
});
Comment on lines 75 to 80
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@macroscopeapp macroscopeapp bot Mar 21, 2026

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🟢 Low Layers/GitService.ts:75

When truncateOutput is false, the code throws an error with the message "output exceeded ${maxOutputBytes} bytes and was truncated." — but the output was not truncated; an error was thrown instead. This is misleading because it contradicts the actual behavior. Consider removing the "and was truncated" clause from the error message when truncation is disabled.

           detail: `${quoteGitCommand(input.args)} output exceeded ${maxOutputBytes} bytes and was truncated.`,
🚀 Reply "fix it for me" or copy this AI Prompt for your agent: 
In file apps/server/src/git/Layers/GitService.ts around lines 75-80:

When `truncateOutput` is `false`, the code throws an error with the message `"output exceeded ${maxOutputBytes} bytes and was truncated."` — but the output was not truncated; an error was thrown instead. This is misleading because it contradicts the actual behavior. Consider removing the `"and was truncated"` clause from the error message when truncation is disabled.

Evidence trail:
apps/server/src/git/Layers/GitService.ts lines 66-80 at REVIEWED_COMMIT - Line 66-73 shows truncation logic when `truncateOutput` is true. Line 74-80 shows error throwing when `truncateOutput` is false, with the error message at line 78-79 saying `output exceeded ${maxOutputBytes} bytes and was truncated.` despite no truncation occurring.

}
bytes = nextBytes;
text += decoder.decode(chunk, { stream: true });
}),
).pipe(Effect.mapError(toGitCommandError(input, "output stream failed.")));

text += decoder.decode();
return text;
return { text, truncated };
});

const makeGitService = Effect.gen(function* () {
Expand All @@ -77,6 +98,7 @@ const makeGitService = Effect.gen(function* () {
} as const;
const timeoutMs = input.timeoutMs ?? DEFAULT_TIMEOUT_MS;
const maxOutputBytes = input.maxOutputBytes ?? DEFAULT_MAX_OUTPUT_BYTES;
const truncateOutput = input.truncateOutput ?? false;

const commandEffect = Effect.gen(function* () {
const child = yield* commandSpawner
Expand All @@ -90,8 +112,8 @@ const makeGitService = Effect.gen(function* () {

const [stdout, stderr, exitCode] = yield* Effect.all(
[
collectOutput(commandInput, child.stdout, maxOutputBytes),
collectOutput(commandInput, child.stderr, maxOutputBytes),
collectOutput(commandInput, child.stdout, maxOutputBytes, truncateOutput),
collectOutput(commandInput, child.stderr, maxOutputBytes, truncateOutput),
child.exitCode.pipe(
Effect.map((value) => Number(value)),
Effect.mapError(toGitCommandError(commandInput, "failed to report exit code.")),
Expand All @@ -101,7 +123,7 @@ const makeGitService = Effect.gen(function* () {
);

if (!input.allowNonZeroExit && exitCode !== 0) {
const trimmedStderr = stderr.trim();
const trimmedStderr = stderr.text.trim();
return yield* new GitCommandError({
operation: commandInput.operation,
command: quoteGitCommand(commandInput.args),
Expand All @@ -113,7 +135,13 @@ const makeGitService = Effect.gen(function* () {
});
}

return { code: exitCode, stdout, stderr } satisfies ExecuteGitResult;
return {
code: exitCode,
stdout: stdout.text,
stderr: stderr.text,
stdoutTruncated: stdout.truncated,
stderrTruncated: stderr.truncated,
} satisfies ExecuteGitResult;
});

return yield* commandEffect.pipe(
Expand Down
3 changes: 3 additions & 0 deletions apps/server/src/git/Services/GitService.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -19,12 +19,15 @@ export interface ExecuteGitInput {
readonly allowNonZeroExit?: boolean;
readonly timeoutMs?: number;
readonly maxOutputBytes?: number;
readonly truncateOutput?: boolean;
}

export interface ExecuteGitResult {
readonly code: number;
readonly stdout: string;
readonly stderr: string;
readonly stdoutTruncated?: boolean;
readonly stderrTruncated?: boolean;
}

/**
Expand Down
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