feat: add per-task file-based history store for cross-instance safety

[roomote]

When Roo Code runs in two VS Code windows simultaneously, both instances share a single taskHistory array in globalState. Every write replaces the entire array, so concurrent read-modify-write cycles cause silent data loss.

Solution

This PR introduces TaskHistoryStore, a service that stores each task's HistoryItem as an individual JSON file in its existing task directory (globalStorage/tasks/<taskId>/history_item.json). Cross-process safety comes from safeWriteJson's proper-lockfile on per-task file writes.

Key changes

• New TaskHistoryStore class (src/core/task-persistence/TaskHistoryStore.ts)

  • Per-task file writes via safeWriteJson (source of truth)
  • Index file (_index.json) for fast startup reads
  • Reconciliation logic to detect and fix drift between instances
  • fs.watch for cross-instance reactivity
  • Debounced index writes (2s window) for streaming performance
  • In-process write lock (replaces withTaskHistoryLock from ClineProvider)

• Migration from globalState

  • On first startup, backfills history_item.json from existing globalState("taskHistory")
  • Migration is idempotent and safe to re-run

• Backward compatibility

  • Write-through to globalState("taskHistory") during transition period
  • Fallback lookups from globalState when store does not have an item
  • Allows safe downgrade to older versions

• ClineProvider integration

  • updateTaskHistory(), deleteTaskFromState(), deleteTaskWithId(), getTaskWithId(), getRecentTasks(), getStateToPostToWebview(), handleModeSwitch(), persistStickyProviderProfileToCurrentTask() all use the store
  • Removed taskHistoryWriteLock and withTaskHistoryLock() (lock moved into store)

Test coverage

• 23 unit tests for TaskHistoryStore (upsert, delete, reconcile, migration, invalidation, serialization)
• 5 cross-instance tests (two stores on same path, reconciliation detection, delete detection)
• All 46 existing ClineProvider tests pass (taskHistory, sticky-mode, sticky-profile)

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View task on Roo Code Cloud

[roomote]

Rooviewer   See task

All 3 concurrency issues from earlier reviews remain addressed. Commit 8941c61 debounces the globalState write-through (5s window) instead of writing on every mutation -- the debounce pattern is sound and tests are updated accordingly. No new issues found.

• reconcile() mutates the cache without acquiring withLock, allowing races with upsert()/delete() at async boundaries (e.g., a just-deleted entry can be re-added by a concurrent reconcile)
• taskHistoryStoreInitialized flag is set but never checked -- store consumers (getStateToPostToWebview, getRecentTasks, etc.) can read an empty cache before initialize() completes, causing a briefly empty task history on startup
• The globalState write-through in updateTaskHistory is no longer serialized -- concurrent calls can write stale snapshots to globalState, which matters for the backward-compatibility downgrade path

Previous reviews

• 6b80bb8: Review #1
• 8e5f0b2: Review #2
• ab30708: Review #3

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