[ptr727]

Summary

Settles #1094. menu.ps1 serialized the shared hub cache with a named .NET Mutex, while menu.sh takes a flock on $DIR/hub.lock, so a menu of each kind sharing one cache directory never saw the other's lock.

• menu.ps1 now locks hub.lock itself, opened with FileShare.None, the shape bootstrap.ps1's Lock-Directory already uses. .NET implements that as flock(LOCK_EX|LOCK_NB) on Linux, which conflicts with menu.sh's shared reader lock and its exclusive writer lock in both directions. On Windows it refuses any other open handle on the file. Every caller still takes one exclusive lock, as with the mutex.
• The open does not block on either platform, so a held lock is waited out by retrying. It retries only where the HResult says the file is held, measured on pwsh 7.4: 0x80070020 (low word 32, or 33 for a lock violation) on Windows, and raw errno 11 (EWOULDBLOCK) on Linux. Any other failure, the cache directory's own creation included, fails the task and returns the caller's own failure value. A $false there would read as exit code 0 to a caller comparing with -eq.
• The lock is re-entrant within a session. Invoke-FetchHub is reached through Confirm-HubRoot from inside a span that already holds it, which the mutex allowed and a second open of the file would not.
• -DryRun runs unlocked, matching menu.sh's hub_read_lock_acquire, since a dry run never fetches or reads the cache and must not create the directory or the lock file.

Verification

• TestPowerShellMenuHubLock, 7 cases. On Linux (pwsh 7.4.2 in the offline python:3.12-slim image): all 7 pass, including the two cross-tool cases, a shared flock making the menu wait and the menu's lock refusing a shared flock. On Windows (pwsh 7, from Git Bash): 5 pass, and the 2 Linux-only cases skip.
• Mutations, each failing the suite: FileShare.Read in place of None (3 failures on Linux), the re-entrancy guard removed (the nested case times out), and the New-Item catch removed.
• tests.test_bootstrap passes on Windows. ruff, mypy, PSScriptAnalyzer, the prose gate, and the EOL gate are clean.
• Three local strict-review passes. The first two raised five findings: dry run writing files, an unbounded wait on any plain IOException, an uncaught directory-creation failure ending the session, and two test gaps. Four were fixed in this branch. One was declined: a test for a non-contention IOException, which no portable fixture produces. The wait tests cover that classification from the other side. The third pass raised nothing.

The comments label stands for the new lock's comments.

Closes #1094 on promotion.

🤖 Generated with Claude Code

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.40%. Comparing base (afc77cb) to head (1706fbd).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2537   +/-   ##
========================================
  Coverage    58.40%   58.40%           
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  Files           16       16           
  Lines         8090     8090           
========================================
  Hits          4725     4725           
  Misses        3365     3365           

Flag	Coverage Δ
python-3.13	58.40% <ø> (ø)

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[Copilot]

🟡 Changes recommended

Lock acquisition can wait indefinitely without a timeout or cancellation path.

1 open finding

• Unbounded lock wait can block menu actions indefinitely · New

What changed in this PR

Updates menu.ps1 to coordinate shared hub-cache locking with menu.sh through hub.lock.

Changes:

• Replaces the named mutex with an exclusive file lock.
• Adds retry, failure, dry-run, and re-entrancy handling.
• Adds cross-tool locking and failure-path tests.

File	Summary
tests/​test_bootstrap.py	Adds coverage for PowerShell locking behavior and interoperability.
host-setup/​menu.ps1	Implements shared cache locking and error handling.

🧠 Review effort: Lite

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