[4/4] TUI: reconcile streaming transcript heights

[kevinyang372]

Description

Stack 4 of 4. Fixes two remaining long-transcript streaming costs and the auto-scroll regression exposed by retained viewport layout.

• Streaming animation repaints now reuse a cached agent-block height. Output updates already emit LayoutInvalidated, so actual content changes still trigger measurement.
• A newly rebuilt TuiViewportedList initially queries the end viewport with content_height = 0. Dirty streaming blocks beyond that provisional band are now carried into the next end-clamped query instead of consuming their dirty IDs too early.
• Already-rendered rich blocks are measured through their retained child views, preserving the cached rich-content layout path.

This restores smooth streaming and ensures the streaming tail is painted and auto-scrolled when the final viewport band becomes known.

Release benchmark at 120×50 versus stack PR 3:

• Retained streaming tail, 1,000 rows: ~1.06 ms → 0.0887 ms (91.6% faster).
• Dirty fixed viewport, 1,000 rows: ~1.07 ms → 0.1605 ms (84.9% faster).
• Retained streaming tail, 10,000 rows: 9.88 ms → 0.176 ms (98.2% faster).
• Dirty fixed viewport, 10,000 rows: ~10.6 ms → 1.34 ms (87.4% faster).

Unoptimized absolute costs:

• Retained streaming tail: 0.792 ms at 1,000 rows; 2.17 ms at 10,000 rows.
• Dirty fixed viewport: 0.604 ms at 1,000 rows; 4.17 ms at 10,000 rows.

Stack: #14575 ← #14582 ← #14585 ← 4/4.

Agent conversation: https://staging.warp.dev/conversation/2b6af7be-b227-4b20-aaf4-23c9a8494b81
Stack plan: https://staging.warp.dev/drive/notebook/yM2YcQsILFsFzwixBDbD9p
Performance plan: https://staging.warp.dev/drive/notebook/LHzsFd1B8XbQ8AnUqB88LS

Linked Issue

N/A — Warp Agent CLI long-transcript streaming performance and auto-scroll regression.

• The linked issue is labeled ready-to-spec or ready-to-implement.
• Where appropriate, screenshots or a short video of the implementation are included below (especially for user-visible or UI changes).

Testing

• Added deterministic coverage that animation-only streaming frames reuse height until output is dirty.

• Added deterministic coverage that offscreen dirty streaming height is deferred until the end-clamped viewport band reaches it.

• cargo nextest run -p warp_tui — 903 passed; Nextest reported one unrelated leaky model-menu snapshot test.

• cargo clippy -p warp_tui --all-targets --features test-util -- -D warnings

• cargo bench -p warp_tui --features test-util --bench transcript_bench -- --noplot

• cargo bench --profile dev -p warp_tui --features test-util --bench transcript_bench -- offscreen_streaming_tail --noplot

• ./script/format

• Signed-in live ./script/run-tui: content remained clipped above the input; unsent render-check painted correctly; the UI remained responsive.

• I have manually tested my changes locally with ./script/run-tui

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode

CHANGELOG-BUG-FIX: Fixed choppy streaming and unreliable auto-scrolling in long Warp Agent CLI conversations.

[kevinyang372]

• [4/4] TUI: reconcile streaming transcript heights #14586 👈 (View in Graphite)
• [3/4] TUI: reuse retained text measurements #14585 : 1 other dependent PR (#14594 )
• [2/4] TUI: bound clipped viewport painting #14582
• [1/4] TUI: add retained transcript performance benchmarks #14575
• master

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