fix: remove Unix bash dependency in hook executor

[errfld]

Summary

• switch Unix command execution from bash to portable sh -c
• include shell details in spawn failure errors to improve diagnostics
• add regression tests for shell command construction and spawn error reporting
• document the Unix portability behavior in README

Testing

• cargo test --workspace

Summary by CodeRabbit

• Improvements

  • Use POSIX sh for hook execution on Unix-like systems for better portability.
  • Error messages now include the shell used when command execution fails.

• Documentation

  • Clarified that hooks on Unix-like systems run via sh -c (not Bash-specific).

• Chores

  • Added new issue tracker entries and closed/annotated an existing issue with verification notes.

[coderabbitai]

📝 Walkthrough

Walkthrough

Switches Unix hook execution from Bash to POSIX sh, adds shell-identifying information to command spawn errors and the CommandRunner trait, updates platform helpers to expose a human-readable shell string, and records related metadata and README documentation changes. Tests updated accordingly.

Changes

Cohort / File(s)	Summary
Metadata & Docs \.beads/issues.jsonl, README.md	Added two new issue entries and updated an issue's status/notes; clarified in README that hooks run via POSIX sh -c on Unix-like systems.
Executor: error & trait crates/git-smee-core/src/executor.rs	Error::CommandSpawnFailed now includes a shell: String; CommandRunner gained shell_display(); error construction captures the runner's shell; tests and FakeRunner adjusted to supply/verify shell display.
Platform: shell change & exposure crates/git-smee-core/src/platform.rs	Unix command creation switched from bash to sh; added Platform::shell_display() returning platform-specific strings ("cmd.exe /C" or "sh -c"); tests updated to assert command args and shell display.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• refactor(core): model executor spawn failures explicitly #24: Earlier PR that introduced the CommandSpawnFailed variant and CommandRunner abstraction; closely related to the current extension that adds shell tracking.

Poem

🐰 Hops and thumps for a smaller bash,
Now scripts run under POSIX sh splash.
Errors will whisper which shell took the blame,
Tests nod politely and note the new name.
A carrot of clarity, snug in the frame. 🥕

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title accurately summarizes the main change: switching Unix hook execution from bash to portable sh, which is the primary code change across platform.rs and executor.rs.

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch codex/git-smee-5tx/portable-shell-executor

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In @.beads/issues.jsonl:
- Line 3: The issue record with id "git-smee-5tx" has conflicting metadata:
status is "closed" but the notes say the fix still needs verification; update
the JSONL entry so it is consistent by either setting "status" to "open" (or
"reopened") and adding a clear action item in "notes" to re-verify
platform.rs/spawn usage, or keep "status":"closed" and edit the "notes" and
"close_reason" to confirm the fix landed and the remaining comment removed;
ensure you update the "updated_at" timestamp and, if reopening, add a short
"owner" assignment or comment describing the verification task.

[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In @.beads/issues.jsonl:
- Line 9: The JSONL issue entries embed "Acceptance criteria:" inside the
description instead of using a dedicated acceptance_criteria field—update the
.beads/issues.jsonl entries (e.g., the entry with id "git-smee-h4v") to move the
acceptance criteria out of the description into a top-level
"acceptance_criteria" field, keep the original description text intact minus the
acceptance block, and ensure the parser/loader that consumes these files is
adjusted to read the new acceptance_criteria key (and unit tests or schema
validation updated accordingly) so parsing remains backward compatible for
entries that still embed criteria in description.