Use persisted sync intervals as fallback on startup

[mlw]

This makes it so that on startup, if sync fails or the server doesn't set sync interval values, previously persisted intervals will be used.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR modifies full sync interval handling across the sync manager, configurator, and preflight logic. When the server omits or sends 0 for fullSyncInterval, the system now falls back to a persisted daemon-provided interval instead of compile-time defaults. A new property stores the daemon interval during initialization and is updated when the server provides values.

Changes

Cohort / File(s)	Summary
Interval Fallback Handling Source/common/SNTConfigurator.mm, Source/santasyncservice/SNTSyncManager.mm, Source/santasyncservice/SNTSyncPreflight.mm	Core logic changes: SNTConfigurator now treats interval == 0 as "not provided" by clearing the key. SNTSyncManager adds persistedFullSyncInterval property to store daemon-provided interval read during initialization, uses it as fallback in timer rescheduling when server omits value, and updates it during preflight. SNTSyncPreflight only sets fullSyncInterval when server provides positive value (not 0).
Test Coverage Source/santasyncservice/SNTSyncManagerTest.mm, Source/santasyncservice/SNTSyncTest.mm	New test property persistedFullSyncInterval added to test category. Tests verify: (1) daemon interval is captured during initialization, (2) persisted interval is retained when server omits fullSyncInterval, and (3) persisted interval is updated when server provides value.

Sequence Diagram(s)

sequenceDiagram
    participant Init as Initialization Flow
    participant Daemon as Daemon (XPC)
    participant SM as SNTSyncManager
    participant Preflight as Preflight Handler
    participant Server as Server

    Init->>Daemon: synchronousRemoteObjectProxy<br/>(fullSyncInterval callback)
    Daemon-->>SM: callback(daemonInterval)
    SM->>SM: persistedFullSyncInterval = daemonInterval
    Note over SM: Stores daemon-provided interval<br/>as fallback

    SM->>SM: Schedule full sync timer<br/>using persistedFullSyncInterval

    rect rgba(100, 150, 200, 0.5)
    Note over Preflight,Server: Preflight Sync
    Preflight->>Server: Request sync state
    Server-->>Preflight: fullSyncInterval = X
    Preflight->>SM: Update syncState with interval
    end

    rect rgba(150, 100, 200, 0.5)
    Note over Preflight,Server: Server Omits Interval
    Preflight->>Server: Request sync state
    Server-->>Preflight: fullSyncInterval = nil/0
    Preflight->>SM: fullSyncInterval not set
    SM->>SM: Falls back to<br/>persistedFullSyncInterval
    end

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Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

• Fix issue with sync intervals #884 — Changes the same full-sync interval handling code paths in SNTConfigurator, SNTSyncManager, and SNTSyncPreflight for treating 0/unset values and timer rescheduling logic.
• config: Persist sync intervals, display in status #845 — Modifies daemon interval persistence across SNTSyncManager, SNTSyncPreflight, and SNTConfigurator for full-sync and push-notification interval storage.

🚥 Pre-merge checks | ✅ 1 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The pull request has no description provided by the author, making it impossible to assess whether the intent aligns with the changeset.	Add a clear description explaining the purpose, motivation, and impact of using persisted sync intervals as fallback on startup.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main objective: using persisted sync intervals as fallback on startup, which aligns with all the changes across SNTConfigurator, SNTSyncManager, SNTSyncPreflight, and test files.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch mlw/sync-init-with-persisted-intervals

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