fix(monitor): prevent dashboard poller effect loops

[GT-610]

What this changes

• Stop Poller.start() from reading reactive response data, so callers inside a Svelte $effect do not subscribe to the data that the poller later writes.
• Add a Svelte effect harness and regression test that verifies a completed fetch does not immediately restart its poller.

Fixes #1481

How it was tested

• npm test -- --run (10 test files, 73 tests)
• npm run lint
• npm run build (svelte-check: 0 errors and 0 warnings; production Vite build succeeded)
• Red/green check: the new regression test fails with the removed reactive read restored and passes with this change.

Checklist

• make analyze and make test pass (not run; the Flutter app is unchanged)
• make gen was run, if any model / ARB file changed (not applicable)
• cargo test --workspace passes, if anything under crates/ or monitor/ changed (not run; Rust code is unchanged)
• No formatter was run over untouched code

Summary by CodeRabbit

• Bug Fixes

  • Polling now restarts reliably without changing the loading state based on whether existing data is available.
  • Prevented enclosing Svelte effects from being unnecessarily triggered by polled data updates.

• Tests

  • Added coverage for poller lifecycle management and effect subscription behavior.

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📥 Commits

Reviewing files that changed from the base of the PR and between 15b43e1 and e57121d.

📒 Files selected for processing (3)

• monitor/frontend/src/lib/poller.svelte.ts
• monitor/frontend/src/tests/fixtures/PollerEffectHarness.svelte
• monitor/frontend/src/tests/poller.test.ts

💤 Files with no reviewable changes (1)

• monitor/frontend/src/lib/poller.svelte.ts

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📝 Walkthrough

Walkthrough

Poller.start() no longer sets loading by reading existing poller data. A new Svelte harness resets, starts, and stops a numeric poller through $effect. A test renders the harness, waits for the first fetch, verifies one request, and unmounts the view.

Priority: ⬆️ High

Change: Bug fix · Severity of issue fixed: High

Merge Risk: ⚪ Minimal · up to e5712

The poller now avoids self-triggering effect loops, preserving normal polling intervals and dashboard loading behavior.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: preventing dashboard poller effect loops.
Linked Issues check	✅ Passed	Issue #1481 requires the poller effect to stop self-triggering after fetch completion and to preserve the configured polling interval. Poller.start() no longer reads data, so the enclosing Svelte …
Out of Scope Changes check	✅ Passed	The changes are limited to the poller behavior and focused regression coverage. The harness and tests directly validate the fix for issue #1481. No unrelated implementation change is shown.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1…

✨ 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 fix/monitor-poller-effect-loop

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