Commit 81aa587 (joined-card dock refactor) hardcoded dockProgress={1}
on SessionTodoDock and removed the parent-side spring that drove it,
so the dock popped in the moment props.state.dock() flipped true
instead of sliding/fading in from 0.

Restore the mount animation:
- session-composer-region: re-introduce a useSpring tracking dockOpen,
  keep the segment mounted while it animates out (dockMounted memo),
  pass the spring value through as dockProgress.
- session-todo-dock: multiply dock() into the max-height expression
  so the segment slides 0 → collapsed-height (or 0 → full when
  mounting in expanded state), in addition to the existing opacity
  drive that was already wired.

Composer-dock spring options now appear in three places (Todo
collapse, useDockCollapse for Followup/Revert, and segment mount).
Extract them into a single DOCK_MOTION constant in composer/motion.ts
so the contract is referenceable, not scattered. Pinning the value
(0.3s, bounce:0) is the de facto standard across composer springs;
hoisting to a global SPRING_TOKENS tier ladder and wiring spring
through prefers-reduced-motion are tracked in #34.

Critical:
- dock-card: stop concatenating split.class into a single classList key.
  "foo bar" was becoming a literal token and tripping
  Element.classList.toggle (DOMException). Solid merges class+classList
  natively when both are passed; restored to that idiom for DockCard,
  DockSegment, and DockSegmentForm.

Major:
- editor-serialize: skip the block-separator newline when visit() has
  already contributed one (e.g. an empty <div><br></div>). Fixes
  multiline draft round-trips that were inflating "foo\n\nbar" into
  "foo\n\n\nbar".
- model-picker: nested ThinkingLevel popover renders into Kobalte.Portal,
  so its content sits outside the outer Content's DOM subtree. The
  outer popover's onPointerDownOutside fired on every inner-popover
  click and dismissed the model picker. Both popovers carry
  data-picker-content; outer now ignores the dismiss when
  event.target.closest("[data-picker-content]") matches a nested
  picker.
- session-composer-region: permission requests can arrive while
  prompt.ready() is still false (e.g. switching into a session whose
  prompt is hydrating). The hydrate fallback used to show only the
  loading card, leaving the user no way to approve or deny. The
  fallback now renders SessionPermissionContent when a request is
  pending and falls through to the loading card otherwise.
- send-button: SendButtonProps declared style?: JSX.CSSProperties |
  string but the merge silently dropped the string branch. No caller
  passes a string today, so narrow the prop type to JSX.CSSProperties
  to match actual behavior instead of inventing a string-merge code
  path.

Minor:
- keydown: the Enter-without-Shift branch had if (stopping())
  handleSubmit / else handleSubmit — both arms identical, so the
  conditional was dead. Inlined to a single handleSubmit call. The
  stopping accessor stays in scope for the keydown probe.
- popover-controllers: include cmd.source in the custom slash command
  id so workspace + user configs sharing a command name don't collapse
  into one entry under useFilteredList.

Medium (gemini):
- use-dock-collapse: contentRef is now a signal driven by the JSX ref
  callback, and createResizeObserver consumes that signal directly
  rather than running inside a createEffect. Idiomatic and tracks
  ref re-assignment correctly.

Push back:
- model-picker module-level externalOpen / openModelPicker(): the
  signal is a deliberate imperative API consumed by use-session-commands
  and the prompt-input keybind; multi-composer support would require
  reshaping the call surface, not just the state. YAGNI for the single
  composer this app has today; tracked under #34.
- editor-input draft carryover preserves text only: pre-existing
  intentional design from PR #185 (commit ea01514 "carry plain-text
  draft across directory switch"). Cross-workspace pill resolution
  needs workspace-aware path semantics — out of slice 10 scope.

The composer-slice-10 spec asserted boundingBox 32px but the actual
SendButton renders h-[30px] w-[30px] and DESIGN.md commits to the 30
dense tier. The assertion slipped through CI because it lacks the
@smoke tag the smoke job filters on; it would have failed the moment
someone ran the full e2e shard. Caught in external code review.

Push back deferred: openModelPicker() module-level externalOpen as
P3 follow-up — same reasoning as the prior round. The single-composer
path cleans externalOpen on onOpenChange(false), and a multi-composer
fix needs a mounted registry / focus-aware dispatch redesign rather
than a state shape tweak. Tracked under issue #34.

Slice 10 of issue #440 — full composer + dock + model picker rewrite. 38 commits squashed.

## Highlights

- **Composer joined-card shell**: new DockCard + DockSegment primitives in @opencode-ai/ui, dock widgets share the L34 joined-card layout. Hybrid composer shell renders permission UI inline.
- **prompt-input.tsx 1602 → ~570 lines**: split into prompt-input/{store-types, editor-serialize, editor-imperatives, comment-routing, history-navigation, popover-controllers, editor-input, keydown, model-controls}. No behavior change — all factories injected via deps; popover↔editor-input cycle resolved via mutable forward-ref.
- **DockWidgetHeader unified**: single 36px collapsed header with 30px chev IconButton (3+3 breathing) — consolidates Followup, Revert, Todo widgets.
- **DOCK_MOTION contract**: composer/dock/widgets share `{ visualDuration: 0.3, bounce: 0 }` via packages/app/src/pages/session/composer/motion.ts. Aligns with global useSpring convention.
- **Model picker rewrite**: variant control merged into model trigger; thinking-level promoted from separate popover to inline section. `[data-picker-content]` guard prevents nested popover dismiss.
- **Send button + ContextUsage parity**: 30px outer / 16px inner glyph, theme-locked colors, larger stop glyph.
- **Followup defaults to queue mode**: drops the legacy steer override.
- **Control heights**: single 30px dense tier across composer; sidebar trailing actions step down to 26 per nesting rule.
- **Picker contracts**: tighter padding, narrower width (340), dropped sticky labels.

## Post-review fixes (CI + 2 review rounds)

- Critical: DockCard manual classList merge (single key with spaces) was throwing DOMException InvalidCharacterError — replaced with Solid native class+classList co-rendering.
- CI typecheck: PopoverControllers types aligned with upstream solid-list `Accessor<string | null>` (was `undefined`).
- CI e2e: dropped stale `prompt-variant-control` selector (variant folded into model picker).
- Send button e2e contract: 32 → 30px to match dense tier.
- Editor serialize: fixed double-newline regression for blank rows.
- Keydown: removed dead `if (stopping())` branches (both arms identical).
- Custom slash command id includes source to prevent workspace+user collision.
- Model trigger label: pinned to `min-w-[80px] max-w-[180px]` to balance short names ("GPT-5.5") vs long ("DeepSeek V4 Pro") without jiggling the workspace control.

## Systemic finding (tracked under #34)

PawWork sets `html { font: var(--type-body) }` → root font-size 13px. This means **Tailwind rem-based units render at 81% of their pixel-named values**: `h-9` = 29.25px, not 36px. Multiple visual bugs in this slice (chev clipping, header height) traced back to this. Remediation: use absolute pixels (`h-[36px]`) for grid-pinned heights; avoid Tailwind's pixel-named scale for 4pt-grid alignment. DESIGN.md docs debt to be filed under #34.

## Hand-test backlog (open after merge)

- #32 dark theme regression sweep
- #33 single-prompt E2E

## Files of note

- packages/ui/src/components/dock-card.tsx (new)
- packages/app/src/pages/session/composer/{motion.ts, use-dock-collapse.ts, dock-widget-header.tsx, session-composer-region.tsx, session-todo-dock.tsx}
- packages/app/src/components/prompt-input/* (9 new files)
- packages/app/e2e/composer/composer-slice-10.spec.ts (new)

Closes part of #440.