fix(web): clarify sidebar drag dividers and empty targets

[juliusmarminge]

Dragging the last thread out of Active or Settled left no visible empty drop target. Divider labels also used boxed styling that did not match the existing section headers.

Keep empty targets mounted at zero height and reveal their dashed boxes when the dragged thread leaves the section. Reveal them directly in place, without the sortable slide transition. Divider labels now use plain text and a line; Settled highlights its text and line rather than drawing another dashed box.

Verified with 239 focused sidebar tests, web typecheck, and browser checks for leaving/returning to the last-thread section and cancelling back to idle. Targeted lint and React Doctor report existing Sidebar warnings. This affects the sidebar shared by web and desktop; no wire, provider, or mobile changes.

Matching 1280 × 720 captures from main f5fb056d248 and head 1c0d4e8a968, using the same thread snapshot and gesture.

Before	After

The recording moves the last Active thread toward Settled, returns it, leaves again, and cancels. Empty targets appear in place and the idle layout recovers.

https://gh-file-drop-api-prod-mi5fy3sowv63ufte.pinglabs.workers.dev/f/ee5214b732055bfb/motion.mp4

Authored with GPT-6 in Codex.

Summary by CodeRabbit

• Bug Fixes

  • Empty sidebar sections now display placeholders correctly when their final item is moved or returned.
  • Dragging items between sections provides more consistent placeholder visibility.

• Style

  • Sidebar placeholders appear without unintended movement animations.
  • Section labels use simpler text styling.
  • Shelf headers no longer show dashed borders or drop-area backgrounds.

[macroscopeapp]

Approvability

Verdict: Would Approve

Macroscope's review found this PR approvable — This is a narrowly scoped sidebar drag UI fix that keeps empty targets measurable, corrects their reveal behavior, and clarifies divider styling. The runtime impact is confined to drag presentation and layout projection, with regression coverage for both affected sections.

Not approved because:

• Monthly spending limit reached (workspace setting). Approvability relies on correctness review in order to determine eligibility

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.5 KiB	13.6 KiB	+72 B (+0.5%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.0 KiB	7.0 KiB	+2 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.6 KiB	+70 B (+1.1%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	57.1 KiB	+88 B (+0.2%)	66.4 KiB	✅
Codex	Live turn messages	8	10	+2 (+25.0%)	21	✅
Claude	Total thread wire	13.6 KiB	13.6 KiB	−27 B (−0.2%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.0 KiB	−4 B (−0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.6 KiB	6.5 KiB	−23 B (−0.3%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.9 KiB	57.8 KiB	−44 B (−0.1%)	66.4 KiB	✅
Claude	Live turn messages	10	9	−1 (−10.0%)	21	✅

Baseline: f5fb056 · PR result: 1c0d4e8 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 113.9 KiB
• Claude decoded thread snapshot: 114.6 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

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Review profile: CHILL

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Run ID: 22f636c2-f8d4-4de5-9540-2ef412c373e8

📥 Commits

Reviewing files that changed from the base of the PR and between f5fb056 and 1c0d4e8.

📒 Files selected for processing (2)

• apps/web/src/components/Sidebar.drag.test.ts
• apps/web/src/components/Sidebar.tsx

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📝 Walkthrough

Walkthrough

The sidebar drag-and-drop UI now keeps active and settled placeholders mounted, controls their visibility during cross-section dragging, disables reveal transitions, and simplifies boundary styling. Tests cover revealing and rehiding empty section placeholders.

Changes

Sidebar drag placeholder behavior

Layer / File(s)	Summary
Placeholder projection and visibility apps/web/src/components/Sidebar.tsx, apps/web/src/components/Sidebar.drag.test.ts	Active and settled placeholders remain in sortable item sequences. Visibility now depends on empty sections and sole-row transfers. Tests cover revealing and rehiding placeholders.
Placeholder and boundary presentation apps/web/src/components/Sidebar.tsx	Revealed placeholders disable transitions. Drag boundary labels and shelf headers use simplified styling.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 1c0d4

Sidebar empty drop targets now remain mounted and appear during sole-row cross-section drags without slide transitions. No material merge risk remains.

Suggested reviewers: sunkenintime, t3dotgg

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the sidebar divider styling and empty drop-target fix.
Description check	✅ Passed	The description explains what changed and why, includes before/after UI captures and an interaction recording, and documents verification results and scope. It provides the required information even w…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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