Serialise users store access with a lock

[Sloth-on-meth]

Problem

Every UsersStore operation is load → mutate → save on shared instance state (self.data), and gunicorn runs 4 threads. A touch_user() (every successful door open) racing an admin edit can write back a stale snapshot and silently undo the edit, e.g. re-enable a user an admin just disabled, or drop a freshly created user. effective_pins() also swaps self.data while another thread may be iterating it.

Changes

• Added a re-entrant lock and a @_locked decorator applied to every public method, so each load-mutate-save runs atomically with respect to other threads. No change to storage format or behaviour.

Tests

tests/test_users_store_concurrency.py: a toucher thread hammering touch_user while the main thread toggles active (disable is never lost), and 4 threads × 25 touches count exactly 100. Both tests fail when the decorator is removed. Full suite passes (110), ruff clean.

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Summary by CodeRabbit

• Bug Fixes
  • Improved reliability when account operations run at the same time. Disabling an account is no longer undone by a concurrent update, and overlapping activity is accurately counted. Public account-store operations are serialized to help keep results consistent during concurrent use.

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• tests/test_users_store_concurrency.py
• users_store.py

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📝 Walkthrough

Walkthrough

UsersStore now wraps every public method with a per-instance reentrant lock. New tests check concurrent user status changes, concurrent touch counts, and which methods are wrapped.

Changes

UsersStore concurrency

Layer / File(s)	Summary
Locking and concurrency validation users_store.py, tests/test_users_store_concurrency.py	A _locked decorator serializes public UsersStore methods with an instance reentrant lock. Tests check concurrent status changes, verify that 100 concurrent touches increment times_used to 100, and confirm that _load_file is not wrapped.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~12 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 9afc1

The per-instance locking change is ready to merge after normal checks.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 9afc1

The lock improves protection against concurrent user updates in the configured deployment. It protects calls through one store instance, not independent instances or processes. No introduced security regression was identified, but other deployment configurations and independent writers remain unverified.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• observed — The changed control protects shared user records and effective PIN data used by the application. Its exclusion boundary is one UsersStore object, not the persisted file across all possible writers.

Trust Boundaries and Controls

• observed — The routed test adds no attacker-facing interface. Production callers continue using the same store methods; the added control serializes execution rather than granting new authority or changing authentication inputs.

Resilience and Maintainability Implications

• inferred — The lock context releases ownership on normal and exceptional exits, and reentrancy avoids self-deadlock for nested same-thread calls. Separate instances retain independent locks, so cross-instance lost updates remain a pre-existing limitation.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 42.86% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 7 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: serializing UsersStore access with a lock.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

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Inline comments:
Review comments at @tests/test_users_store_concurrency.py:
- Line 30: Update the persistence assertions in the concurrency test to read
values through a fresh UsersStore instance opened on the same file, while
keeping all worker threads on the original store instance.

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• Configuration used: defaults
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• tests/test_users_store_concurrency.py
• users_store.py

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[Sloth-on-meth]

Merge-conflict fix (9afc16a), no behaviour change: the lock is now applied in one block at the end of users_store.py (every public method is wrapped; methods added later are locked by default, with a test) instead of a decorator on each def and a line in __init__. That removes the textual overlap with #48 and #49, so all open PRs now merge cleanly in any order. Verified by merging all of them together in forward, reverse and shuffled order: no conflicts, 167 tests pass.

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