[BUG] PreToolUse hook `updatedInput` is silently ignored for the Bash tool

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Bug report: PreToolUse hook updatedInput is silently ignored for the Bash tool

Claude Code version: 2.1.215 (desktop app)
Area: PreToolUse hooks — hookSpecificOutput.updatedInput on the Bash tool

Summary

A PreToolUse hook that returns permissionDecision: "allow" together with
updatedInput to rewrite a Bash command has no effect — the original,
unrewritten command runs. This holds even for a single hook (no sibling
interaction required), and even when every matching hook emits updatedInput
and none emits an empty/no-updatedInput response.

The documented behavior is that updatedInput modifies the tool's input
parameters. For the Bash tool in this build, it is silently dropped.

Isolation (this was verified by elimination, not assumed)

Setup: four PreToolUse hooks match Bash (a command-rewriter + three validator
hooks). Symptom: the rewriter's updatedInput never applies.

1. Symptom: rewriter's updatedInput (command → rtk <cmd>) never applied;

commands ran raw.

1. Ruled out "empty-abstain sibling clobbers a rewriter": made all three

validator hooks emit an explicit decision-less envelope
{"hookSpecificOutput":{"hookEventName":"PreToolUse"}} instead of bare
exit 0. The rewrite still did not apply.

1. Ruled out sibling interaction entirely (decisive): made ALL FOUR Bash

hooks emit updatedInput for one probe command (git status --probe →
echo MARKER), each with permissionDecision: "allow". No hook emitted a
no-updatedInput response. The probe command STILL executed raw
(git: unknown option 'probe') — neither the marker rewrite nor the proxy
rewrite applied.

Since no empty/abstaining response was present in step 3, sibling-clobbering
cannot explain it: updatedInput is simply not honored for the Bash tool in
this session. Each hook was confirmed to emit well-formed JSON when invoked
directly, so the hooks fired and their output was ignored.

Actual

The original command runs; updatedInput is silently discarded for Bash.

Impact

Any transparent Bash command-rewriter hook (proxies, token optimizers, sandbox
wrappers, redactors) silently no-ops. If the rewrite is a policy control, it's a
silent policy bypass with no signal to the user or the hook.

What Should Happen?

The hook's updatedInput.command is applied; the rewritten command runs.

Steps to Reproduce

Minimal, single hook

.claude/settings.json:

{"hooks":{"PreToolUse":[{"matcher":"Bash","hooks":[{"type":"command","command":"node rewrite.mjs"}]}]}}

rewrite.mjs:

process.stdout.write(JSON.stringify({hookSpecificOutput:{hookEventName:"PreToolUse",permissionDecision:"allow",updatedInput:{command:"echo REWRITE_APPLIED"}}}));

Run any Bash command → expected REWRITE_APPLIED, actual: the original command runs.

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.207 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Claude Code desktop app (Windows) — commands run via its Bash tool = Git Bash (MINGW64), not an interactive shell

Note vs. existing issues

• Distinct from #30770 (single hook's partial updatedInput replacing fields

instead of merging — closed not-planned). Here updatedInput has NO effect at
all.

• Distinct from #75915 (sibling returns ask + user approves → updatedInput

dropped). No ask and no prompt is involved here.

• Possibly related to #47853 ("updatedInput silently ignored for Edit — works

for Read and Bash"), but INVERTED: Bash is also ignored in this 2.1.215
desktop build. If Bash updatedInput is expected to work, this may be a
regression or a build/platform-specific defect.