feat: improve sync responsiveness (v1.3.0)

[psimaker]

Closes #4.

Summary

• Lower the per-folder RescanIntervalS from 3600 s to 60 s (Syncthing's own default). Existing folders carrying the legacy 3600 are migrated on bridge start; user-customised values are preserved.
• Auto-trigger a foreground rescan when the scene returns to .active after the app was backgrounded for ≥5 s, so edits made in Obsidian on iOS show up without the close-and-reopen workaround.
• Add pull-to-refresh on the main vault list as a deliberate, low-noise manual sync hook (no dedicated button on the home screen).

Addresses the issue surfaced on Reddit by u/wet_tank. Cloud Relay does not cover the iPhone → desktop direction (notify lives on the desktop), so the fix lives entirely on the iOS / bridge side.

Test plan

• Go bridge unit tests (rescan_migration_test.go): default = 60, legacy 3600 → migrated to 60, custom 120 preserved.
• Swift unit tests (ForegroundRescanDebounceTests): predicate fires above threshold, skips below, handles nil, fires at exact boundary.
• Full Go bridge suite green.
• Full iOS test suite (36 tests) green.
• Manual: pull-to-refresh gesture on main vault list triggers a sync.
• Manual: background app >5 s → return → auto-rescan fires. Background <5 s → return → no rescan.
• Manual: existing on-device install with at least one vault → after this build, that vault's RescanIntervalS is 60.

This PR improves iPhone → desktop sync responsiveness by reducing fallback rescan latency, adding a foreground rescan when the app returns from background, and exposing a manual pull-to-refresh.

User-visible sync behavior

• New folders now use a 60 s rescan interval (Syncthing default) instead of 3600 s.
• Existing folders with the legacy 3600 s value are migrated to 60 s at bridge startup; any user-customized rescan intervals are preserved.
• When the app returns to .active after being backgrounded for ≥5 s, the app triggers an immediate foreground rescan so edits made in Obsidian on iOS surface on desktop without restarting VaultSync.
• Main vault list gains pull-to-refresh as a manual sync trigger.

Implementation highlights

• Go bridge: introduced defaultRescanIntervalS = 60, updated AddFolder and AcceptPendingFolder to use it, and added a startup migration in StartSyncthing that replaces legacy 3600 s values with 60 s while preserving custom values.
• iOS app: track lastBackgroundedAt in VaultSyncApp; added BackgroundSyncService.shouldRescanOnForeground(now:lastBackgroundedAt:threshold:), an async SyncthingManager.performForegroundSync(folderID:) wrapper, and a .refreshable pull-to-refresh on the main vault list.
• Documentation: bump to v1.3.0 and list these changes in README/CHANGELOG.

Privacy / security impact

• No new network endpoints or background upload behavior introduced. The changes only alter rescan timing and foreground-triggered syncs; user data handling and Syncthing security model are unchanged.

Background execution impact

• Foreground rescan is triggered only when returning to .active after a threshold and is gated by existing bridge-running/sync-in-progress checks. Existing background assertion and continued-processing behavior remain unchanged.

Test coverage and outstanding verification

• Added Go tests (3) covering default rescan assignment, legacy-3600→60 migration, and preservation of custom intervals.
• Added Swift tests (4) for the foreground-rescan debounce predicate (nil, below/above/equal-threshold cases).
• CI: unit test suites for Go and Swift are green.
• Manual verification still pending for: pull-to-refresh UX, background-duration-triggered rescan in real-world usage, and migration behavior on existing user installs.

Closes #4.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

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Run ID: aa042769-4d49-4697-9b2e-520696ab0b51

📥 Commits

Reviewing files that changed from the base of the PR and between ec6eadf and 33de8e5.

📒 Files selected for processing (3)

• CHANGELOG.md
• README.md
• ios/project.yml

✅ Files skipped from review due to trivial changes (3)

• CHANGELOG.md
• ios/project.yml
• README.md

📜 Recent review details

⏰ Context from checks skipped due to timeout of 900000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (1)

• GitHub Check: Go Tests

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📝 Walkthrough

Walkthrough

This PR addresses unresponsive sync when editing in third-party apps (e.g., Obsidian) on iOS by reducing the fallback rescan interval from 60 minutes to 60 seconds and triggering responsive foreground rescans. The Go bridge normalizes folder configurations and adds a startup migration, while iOS detects background transitions and optionally rescans with a 5-second debounce threshold.

Changes

Go Bridge Rescan Interval Normalization

Layer / File(s)	Summary
Rescan Interval Constant go/bridge/folders.go	Introduces defaultRescanIntervalS = 60 as the fallback interval for new folder configurations.
Folder Configuration Updates go/bridge/folders.go, go/bridge/pendingfolders.go	AddFolder and AcceptPendingFolder use the default constant instead of hardcoded 3600 when creating new Syncthing folders.
Startup Migration Logic go/bridge/syncthing.go	StartSyncthing iterates configured folders and migrates legacy 3600 intervals to defaultRescanIntervalS, preserving user-customized values.
Go Bridge Tests go/bridge/rescan_migration_test.go	Three tests verify default interval on new folder creation, legacy interval migration, and preservation of custom intervals across restart.

iOS Foreground Sync Trigger

Layer / File(s)	Summary
Foreground Rescan Debounce Predicate ios/VaultSync/Services/BackgroundSyncService.swift	Pure static helper shouldRescanOnForeground evaluates whether elapsed background time meets the rescan threshold.
App State and Scene Lifecycle ios/VaultSync/App/VaultSyncApp.swift	Tracks lastBackgroundedAt on background entry; on foreground, checks debounce predicate and conditionally triggers triggerForegroundSync() with a 5-second threshold.
Async Foreground Sync API ios/VaultSync/Services/SyncthingManager.swift	Adds performForegroundSync() async method for awaitable callers; existing triggerForegroundSync() remains fire-and-forget.
Pull-to-Refresh UI ios/VaultSync/Views/ContentView.swift	Main list now has .refreshable modifier to allow user-initiated foreground sync.
iOS Foreground Debounce Tests ios/VaultSyncTests/ForegroundRescanDebounceTests.swift	Four tests verify debounce predicate behavior: nil handling, above/below threshold, and exact boundary conditions.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

📱 From background dreams to foreground screens,
A gentle nudge when sync convenes—
Five seconds rest, then files align,
No more the 60-minute climb.
Fast folders, fast hearts, a quicker shine. ✨

🚥 Pre-merge checks | ✅ 7

✅ Passed checks (7 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title uses conventional-commit style (feat:) and clearly summarizes the main objective of improving sync responsiveness for v1.3.0.
Linked Issues check	✅ Passed	All coding requirements from issue #4 are met: Go bridge rescan interval changes (default 60s, migration, preservation), iOS app background tracking, foreground rescan trigger, async wrapper, and pull-to-refresh are all implemented with corresponding tests.
Out of Scope Changes check	✅ Passed	All changes directly address the stated objectives (rescan interval, foreground sync, pull-to-refresh). Version bumps and changelog/readme updates are expected release activities, not out-of-scope.
No Private Note Leakage	✅ Passed	Code does not leak sensitive data. No vault paths, note contents, or secrets logged. FolderID marked private. No network calls or crash reporting added.
Bounded Ios Background Work	✅ Passed	iOS background work is properly bounded (max 3s), expiration-aware with registered handlers, respects privacy (no vault data in logs), and manages assertions correctly.
Bridge Contract Compatibility	✅ Passed	Gomobile types, JSON shapes, and empty-string conventions preserved. No exported function signatures changed. Internal constant added. Tests added verify behavior without breaking contract.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/sync-responsiveness

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