fix: prevent spontaneous scroll jumps when reading old messages

[torlando-tech]

Summary

• Remove _messagesRefreshTrigger from the paging flow's combine() — it was creating a brand-new PagingSource every 30 seconds (and on each delivery receipt), discarding all loaded pages and causing the viewport to jump back toward recent messages
• Room's PagingSource already auto-invalidates on DB writes with proper key-based scroll position preservation
• formatTimestamp() is a pure function that recomputes relative times on each recomposition, so no data-layer refresh was ever needed for timestamp updates

Test plan

• MessagingViewModelTest — all pass
• MessagingViewModelImageLoadingTest — all pass
• Manual: open a long conversation, scroll far up, wait 60+ seconds — viewport should stay put

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

This PR removes _messagesRefreshTrigger from the paging combine() in MessagingViewModel, which was forcing a brand-new PagingSource every 30 s and on every delivery receipt — destroying all loaded pages and snapping the viewport back toward recent messages. Timestamp updates are now driven by a Compose-level timestampTick clock passed as a parameter to MessageBubble, triggering recomposition of only visible items without touching PagingData.

Confidence Score: 5/5

Safe to merge — the fix is correct and all remaining findings are style-level.

The root cause (PagingSource recreation on every tick/delivery receipt) is accurately identified and properly fixed. Room's PagingSource reliably auto-invalidates on DB writes; the old workaround comment about cachedIn() blocking propagation was incorrect. The Compose-level timestampTick clock pattern (passing an unused-but-tracked parameter to force recomposition) is a well-established technique. Import reordering and test-mock additions are cosmetic/correctness improvements with no risk.

No files require special attention.

Important Files Changed

Filename	Overview
app/src/main/java/network/columba/app/viewmodel/MessagingViewModel.kt	Removes _messagesRefreshTrigger from combine() and drops the refreshTimestamps() helper; Room's PagingSource auto-invalidation now handles delivery-status and new-message refreshes correctly.
app/src/main/java/network/columba/app/ui/screens/MessagingScreen.kt	Drops LaunchedEffect(timestampTick) { viewModel.refreshTimestamps() }; instead passes timestampTick directly to MessageBubble so Compose recomposes only visible bubbles on each clock tick.
app/src/main/java/network/columba/app/nomadnet/PartialManager.kt	Import block reordered to standard alphabetical Kotlin style; no logic changes.
app/src/main/java/network/columba/app/viewmodel/NomadNetBrowserViewModel.kt	Import block reordered to standard alphabetical Kotlin style; no logic changes.
app/src/test/java/network/columba/app/viewmodel/MapViewModelTest.kt	Adds previously missing mock for settingsRepository.mapStylePreferenceFlow to fix a test compilation/runtime gap.
app/src/test/java/network/columba/app/viewmodel/NomadNetBrowserViewModelTest.kt	Import block reordered to match the source-file style change; no logic changes.
micron/src/test/java/network/columba/app/micron/MicronParserTest.kt	Three method-chain expressions reformatted for readability; no logic changes.

Sequence Diagram

sequenceDiagram
    participant DB as Room DB
    participant PS as PagingSource
    participant VM as MessagingViewModel
    participant SC as MessagingScreen
    participant MB as MessageBubble

    note over VM,SC: BEFORE (causes scroll jumps)
    DB->>PS: DB write (delivery receipt)
    PS-->>VM: invalidate (auto)
    VM->>VM: _messagesRefreshTrigger++
    VM->>PS: new PagingSource created
    note over SC: All loaded pages discarded → scroll jumps

    note over VM,SC: AFTER (this PR)
    DB->>PS: DB write (delivery receipt)
    PS-->>VM: invalidate (auto, key-based)
    note over SC: Scroll position preserved

    loop Every 30 s (RESUMED lifecycle)
        SC->>SC: rememberLifecycleTickerMillis tick
        SC->>MB: timestampTick (new value)
        MB->>MB: recompose → formatTimestamp() re-runs
        note over MB: Only visible bubbles recompose
    end

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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[torlando-tech]

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