Action Fusion reports success for failed then_run commands on Pi 0.99.2/1.0.0 #94

Environment

• SoL-Pi: e1a586af0ad8956f42ae5b26bba20e48fbf30e00
• Reproduced on Pi 0.99.2 and 1.0.0
• Passes on Pi 0.85.1, the version pinned by this repository
• macOS arm64, Node.js 24.14.1, npm 11.11.0

Reproduction

In a temporary checkout at the commit above, install the locked dependencies, then install Pi 1.0.0 without changing the manifests or lockfile:

npm ci --ignore-scripts
npm install --no-save --package-lock=false --ignore-scripts --no-audit --no-fund \
  @earendil-works/pi-coding-agent@1.0.0 \
  @earendil-works/pi-ai@1.0.0 \
  @earendil-works/pi-agent-core@1.0.0 \
  @earendil-works/pi-tui@1.0.0

PI_OFFLINE=1 ./node_modules/.bin/vitest run tests/action-fusion.test.ts \
  -t 'preserves a successful mutation when then_run fails'

The test fails because the fused tool call resolves instead of rejecting. Its result contains:

[then_run:succeeded]
validation failed

Command exited with code 7

The same test fails on Pi 0.99.2 and passes on Pi 0.85.1. I also reproduced this for both edit and write using Pi's extension loader and AgentSession, real local commands, and a deterministic faux provider. No remote model is needed.

Expected behavior

When the follow-up command fails, the fused tool call should report an error while keeping the completed file changes and diagnostic output. Successful commands and calls without then_run should remain unchanged.

Cause

executeMutationThenRun() catches errors thrown by bash, but does not check the isError flag when bash returns a result. Pi 0.85.1 throws for a nonzero command exit; Pi 0.99.2 and 1.0.0 return isError: true. SoL-Pi still appends the success marker and reports the fused tool call as successful.

The command runs and fails; SoL-Pi reports the wrong status. This is separate from #60's savings rendering, #73/#77/#82's shell-path handling, and #67/#80's argument validation.