Prevent scavenger from re-enqueuing items already being picked up

[Reetus]

Tracks pending item serials to skip items already in the action queue. Serials are removed via ContinueWith when the drag/drop action completes (success or failure), allowing retry on next CheckArea pass.

Summary by CodeRabbit

• Bug Fixes
  • Fixed an issue where the scavenger feature could enqueue duplicate drag and drop actions for the same item whilst a previous action was still processing.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 16cf0715-1dc8-452a-9fd5-56b3d8539b96

📥 Commits

Reviewing files that changed from the base of the PR and between 3e09f07 and 7c4e243.

📒 Files selected for processing (1)

• ClassicAssist/UI/ViewModels/Agents/ScavengerTabViewModel.cs

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Walkthrough

Added a concurrency-tracking mechanism using _pendingSerials and _pendingSerialsLock to prevent duplicate drag/drop actions for the same item serial. The CheckArea() method now prunes non-existent items, skips pending serials, records enqueued serials, and removes them upon task completion via ContinueWith.

Changes

Cohort / File(s)	Summary
Scavenger concurrency control ClassicAssist/UI/ViewModels/Agents/ScavengerTabViewModel.cs	Added thread-safe tracking of pending item serials with lock-based synchronisation. Modified CheckArea() to prune stale entries, skip duplicate actions, and clean up serials after EnqueueDragDrop() completes. Prevents concurrent duplicate drag/drop operations for the same item.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% 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 title directly and clearly summarizes the main change: preventing the scavenger from re-enqueueing items that are already being picked up, which aligns perfectly with the concurrency-tracking mechanism introduced.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch scavenger-debounce

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