perf(agents): skip renders for unchanged presence polls

[danielgap]

Summary

• The 1 Hz presence poll in lib/agents-view.ts ended every poll by assigning peers/remoteThreads, calling refreshTasks() + clearFooterLayout(), and unconditionally requesting a render, even when nothing display-relevant had changed. With a live-but-quiet background agent this drove a permanent 1 Hz full-transcript layout pass (the dominant remaining driver of perf: fullscreen mode still re-renders the full transcript on the 1 Hz agents-view presence poll #1011 after fix(fullscreen): avoid duplicate transcript measurement render #1098/feat(ui): unify sidebar status and shell working feedback #1110 landed the layout-side work).
• Every poll now computes a cheap change signature over the poll inputs: peer group ids/labels, per-task display fields (status, agent, model, tokens, cost, timestamps, error), remote thread item shape plus a tail hash of text/output content, and the local task list filtered exactly like refreshTasks(). An unchanged signature skips the state assignment, refreshTasks(), clearFooterLayout(), and requestRender(); the 1 s timer re-arms identically.
• The comparison errs toward rendering: the catch path always renders and re-anchors the signature, and any field outside the signature that could reach the UI is accompanied by its own render driver (audited against sessionGroups(), allRows(), footer gating, and thread view consumption).

Issue

Closes #1011 (approved). This delivers the remaining presence-poll scope the maintainer kept the issue open for after #1098.

Type

• Bug fix
• Performance improvement

Changes

File	Change
lib/agents-view.ts	taskSignature() + presenceSignature() (+ tail hash over last 64 chars of item text/tool output); render gate in the poll commit branch; signature re-anchor in the catch branch (+72/−5)
tests/agents-view-render-gate.test.ts	6 gate tests: quiet poll renders once then polls silently; peer status/label/membership changes render; local store changes render under identical presence; same-length content rewrite renders (tail hash); error path renders and recovers

Verification

• Observed RED on unchanged source for all 6 gate tests (e.g. identical poll rendered twice; same-length rewrite stayed silent).
• Focused: gate suite 6/6, tests/agents-view.test.ts 27/27.
• Full unit suite: 2,616 passed, 0 failed, 10 cancelled (pre-existing tests/rdd-status-line.test.ts environmental cancellations, reproduced on a pristine main checkout; module graph untouched by this diff).
• Provider-contract check passed; runtime harness passed after hydrating the pinned package-local runtime (scripts/install-gentle-ai.mjs).
• Typecheck ratchet: 197 recorded diagnostics, no regressions.
• Polling mechanics unchanged: 1000 ms cadence, setTimeout(step, 0) yield structure, PresenceCursor lifecycle, no new refreshPresence() callers.
• Native consolidated reliability review: approved, 4 informational advisories, no corrections; acknowledgement completed.

Measurements and limits

• Expected effect: with an idle-visible session and a quiet live agent, presence polls no longer schedule layout passes, so the ~1 Hz render bursts measured in the issue disappear while the snapshot is unchanged. Cost per poll is one signature string build over display fields (no serialization of thread content).
• Known limit, deliberate: thread item content contributes length plus a 64-char tail hash, so a hypothetical same-length rewrite that also matches the tail hash would stay silent (probability ~1 in 4e9 per rewrite). Local (own-session) task streaming is unaffected: those renders have their own drivers.

Summary by CodeRabbit

• Bug Fixes
  • Reduced unnecessary interface updates during background presence polling.
  • Ensured visible changes—such as peer status, availability, task updates, or streamed content edits—appear on the next poll.
  • Improved recovery after failed presence checks so remote state and rendering update correctly.

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• lib/agents-view.ts
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📝 Walkthrough

Walkthrough

AgentsView now gates presence-poll renders with a signature of rendered task, peer, group, and thread state. Tests verify silent unchanged polls, detected changes, local updates, membership changes, and failure recovery.

Changes

Presence Render Gate

Layer / File(s)	Summary
Presence signature computation lib/agents-view.ts	Adds signatures for local tasks, peer groups, task metadata, thread shape fields, and fixed-width tail hashes for content changes.
Polling and render validation lib/agents-view.ts, tests/agents-view-render-gate.test.ts	Presence polling requests renders only when signatures change, records cleared error state, and tests quiet polls, state changes, membership changes, local updates, and recovery.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Refactor · Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant PresenceCursor
  participant AgentsView
  participant requestRender
  PresenceCursor->>AgentsView: Read presence state
  AgentsView->>AgentsView: Compare presence signature
  alt State changed or read failed
    AgentsView->>requestRender: Request render
  else State unchanged
    AgentsView->>AgentsView: Re-arm poll timer
  end

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Suggested reviewers: alan-thegentleman

Merge Risk: ⚪ Minimal · up to 14058

The render gate continues to update the view when normal thread content changes while eliminating unnecessary idle renders. No actionable merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 40.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 10 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 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: skipping renders for unchanged presence polls in AgentsView.
Linked Issues check	✅ Passed	The PR meets the coding objective in [#1011]. lib/agents-view.ts gates the 1 Hz presence render path with signatures for peer data, task display fields, remote thread content, and the filtered local…
Out of Scope Changes check	✅ Passed	The changes stay within [#1011]. The production change gates unnecessary presence-poll renders in lib/agents-view.ts. The added tests verify this behavior. The whole-PR summary identifies no unrelat…

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Actionable comments posted: 2

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Inline comments:
In `@lib/agents-view.ts`:
- Around line 234-235: After refreshTasks() in both summary and selected-task
callbacks, update lastPresenceSignature using presenceSignature(this.peers,
this.remoteThreads) before requestRender(). Adjust the local-task test to expect
no additional render during the next poll when remote presence is unchanged.
- Line 139: The taskSignature construction in agents-view.ts is ambiguous
because raw colon delimiters allow field collisions, and presenceSignature can
miss same-length edits before the retained tail. Encode task fields with an
unambiguous structural representation, and include a complete revision of each
rendered thread item's text and output so any content change invalidates the
poll gate. Add coverage for delimiter-colliding task fields and same-length
edits occurring before the final 64 characters.

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Configuration used: Repository UI

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📒 Files selected for processing (2)

• lib/agents-view.ts
• tests/agents-view-render-gate.test.ts

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