[Xuepoo]

Priority: P1 | Area: area:ui | Labels: fix,P1,area:ui | Milestone: v0.1.0 | RFC: plugin UI surface v1 | Task: CTX-1341

Closes #2226

What

Mounting into left/right returned a successful handle but never painted, reserved no columns, and had no hit target. They now map to Unsupported, so the existing mount gate returns typed E_UI_UNAVAILABLE (class runtime) before any handle is minted or block stored.

Changes

• band_slots.rs: left/right placement is Unsupported, message names the slot and the missing vertical band host.
• services.rs: mount comment plus retained-count expectation (top/bottom/overlay).
• plugin_ui.rs: removed the retention lock-in; added vertical_band_slots_fail_closed_at_mount (ok=false, E_UI_UNAVAILABLE, slot-named message, empty registry).
• Code comments synchronized in runtime.rs, band_host.rs, present.rs, bitty-lua/src/ui.rs.

Verification

• fmt, clippy -D warnings (runtime all targets), Windows workspace all-targets: pass
• cargo nextest run -p bitty-runtime --locked: 2524 passed, 1 skipped
• Mutation: restoring Band(Left/Right) fails both the new unit and integration assertions
• No behavior change to top/bottom/overlay, routing, or typed errors

Follow-up

Canonical docs update tracked as bitty-terminal-docs#245 (slot table currently says stored-but-not-painted).

Summary by CodeRabbit

• Bug Fixes
  • Mounting UI elements in the left or right slots now fails with a clear unavailable error. These slots are no longer retained as chrome bands.
  • Top, bottom, and overlay placements remain available.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Repository UI (base), Organization UI (inherited)
• Review profile: CHILL
• Plan: Advanced
• Run ID: 02516ae6-3cc1-44ea-81a0-beddf3560fc0

📥 Commits

Reviewing files that changed from the base of the PR and between f424321 and 319eb2b.

📒 Files selected for processing: 7

• crates/bitty-lua/src/ui.rs
• crates/bitty-runtime/src/plugin_runtime/services.rs
• crates/bitty-runtime/src/runtime.rs
• crates/bitty-runtime/src/runtime/band_host.rs
• crates/bitty-runtime/src/runtime/band_slots.rs
• crates/bitty-runtime/src/runtime/present.rs
• crates/bitty-runtime/tests/plugin_ui.rs

Included review availability: This review used your included allowance. Your plan provides up to 1 included review per hour; 0 remain after this review.

📝 Walkthrough

Left and right UI slots now fail closed with E_UI_UNAVAILABLE because no vertical band host exists. The runtime no longer routes these slots to vertical bands. Updated tests verify rejection and confirm that no UI blocks are retained.

Changes: Vertical UI slot rejection

Layer / File(s)	Summary
Reject vertical slots at mount crates/bitty-lua/src/ui.rs, crates/bitty-runtime/src/plugin_runtime/services.rs, crates/bitty-runtime/src/runtime.rs, crates/bitty-runtime/src/runtime/band_slots.rs, crates/bitty-runtime/src/runtime/band_host.rs, crates/bitty-runtime/src/runtime/present.rs	Left and Right map to unsupported placement. Mounts fail with E_UI_UNAVAILABLE. Documentation describes the top/bottom-only band behavior.
Verify rejection and routing crates/bitty-runtime/src/plugin_runtime/services.rs, crates/bitty-runtime/src/runtime/band_slots.rs, crates/bitty-runtime/tests/plugin_ui.rs	Tests verify unsupported placement, typed errors, empty vertical bands, and no retained UI blocks.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Low

Merge Risk: ⚪ Minimal · up to 319eb

Left and right mounts now report an unavailable-slot error instead of silently succeeding. No actionable merge-blocking issue remains in the supplied evidence.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Linked Issues check		Issue #2226 requires silent success to be impossible, a regression test, retention-test updates, and slot-table documentation sync. The diff maps left and right to Unsupported, preserves typed `…	Update the canonical slot-table documentation required by #2226, or include that documentation change in this PR.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: UI mounts to unwired left and right band slots now fail closed.
Out of Scope Changes check		The implementation changes, comments, retention expectation, and regression tests all support #2226. They change only vertical-slot admission and its related documentation and tests. No unrelated beha…
Docstring Coverage		Docstring coverage is 90.91% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 7 files.

Full details: Out of Scope Changes check

Explanation

The implementation changes, comments, retention expectation, and regression tests all support #2226. They change only vertical-slot admission and its related documentation and tests. No unrelated behavior change is established.

Full details: Linked Issues check

Explanation

Issue #2226 requires silent success to be impossible, a regression test, retention-test updates, and slot-table documentation sync. The diff maps left and right to Unsupported, preserves typed E_UI_UNAVAILABLE errors, and adds unit and integration coverage that verifies failure and an empty registry. The repository slot-table comments are synchronized, but the canonical documentation update remains a separate follow-up (bitty-terminal-docs#245), so the linked issue's documentation acceptance criterion is not complete.

Resolution

Update the canonical slot-table documentation required by #2226, or include that documentation change in this PR.

• Fix all pre-merge checks with AI

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