Merge remote-tracking branch 'origin/main' into port-2619

# Conflicts:
#	packages/ui/src/components/sections/openchamber/OpenChamberVisualSettings.tsx

packages/ui/src/components/chat/composer/DOCUMENTATION.md

@@ -7,6 +7,16 @@ everything between typing and sending.
 own state and wires these modules together; it should not grow logic that
 belongs to one of them.
 
+`ChatContainer.tsx` keeps one `ChatInput` mounted while a new-session draft
+becomes its first session. Draft-only UI first fades for 120ms while the editor
+stays in place. The parent then moves the editor to its final session position
+with a 180ms transform-only FLIP animation. Reduced-motion mode skips these
+transitions. `session-ui-store.ts` marks sessions materialized from a submitted
+draft, so selecting an existing session while a draft is open switches without
+animation. Do not restore separate draft and session composer branches:
+remounting the editor loses focus and interrupts the transition. Keep the
+existing mobile fixed-position rules unchanged.
+
 ## Layers
 
 | Directory | Owns |
@@ -62,6 +72,15 @@ copy.
 exactly what gets sent, so nothing downstream serializes a rich document model
 back into a prompt.
 
+The document is not, however, the string it was given: CodeMirror normalizes
+line endings, so a `\r\n` pair becomes one break and the document ends up
+shorter than the inserted string. **Never derive a caret position from the
+length of text you are inserting** — a caret past the end makes `dispatch`
+throw, the transaction never applies, and the un-normalized text stays in React
+state to crash again on the next restore. Every edit that moves the caret goes
+through `replaceWithCaret` (`editor/documentEdits.ts`), which measures the
+change instead of the string.
+
 The composer previously painted a transparent `<textarea>` over a mirror
 `<div>`. That restricted highlighting to styles which do not change glyph
 advance width — colour, background, underline — because anything else made the
@@ -73,20 +92,54 @@ question of design, not of feasibility.
 Selection rendering: every device runs CodeMirror's `drawSelection()` — it
 keeps typing on the drawn-selection code path, and removing it makes
 CodeMirror enforce cursor association on the native selection, which iOS
-answers with severe input lag. Every device also layers
-`composerNativeSelectionExtension` (`editor/theme.ts`) on top: it re-shows
+answers with severe input lag. **That much is not platform-specific and must
+not be undone.** What differs is who paints the selection, and
+`composerSelectionExtension` (`editor/theme.ts`) picks that per platform.
+
+When CodeMirror 6.43.9's iOS predicate does not match,
+`composerNativeSelectionExtension` layers over `drawSelection()`: it re-shows
 the native selection, and — only while a range is selected — the native caret,
 hiding the painted layers those replace. The native selection is the one that
 shows for two reasons: the painted layer sits behind the content, so tokens
-with their own background (inline code, fences) cover it completely; and
-iOS's selection drag handles attach to the visible native selection and take
-their colour from the caret, so a transparent caret means invisible handles.
-The range-only caret scoping is load-bearing — a native caret visible while
-typing makes WebKit re-render its caret UI after every keystroke, felt as
-severe input lag. The selection tint comes from `--primary`, not the selection
-token:
-themes define `--interactive-selection` with its own alpha, so a translucent
-mix of it is nearly invisible.
+with their own background (inline code, fences) cover it completely; and the
+platform's selection drag handles attach to the visible native selection and
+take their colour from the caret, so a transparent caret means invisible
+handles. The range-only caret scoping is load-bearing — a native caret visible
+while typing makes the browser re-render its caret UI after every keystroke,
+felt as severe input lag.
+
+When CodeMirror 6.43.9's exact iOS predicate matches,
+`composerIOSSelectionExtension` leaves selection-handle geometry and appearance
+to CodeMirror. CodeMirror puts the handles in `.cm-selectionLayer`, normally at
+`z-index: -1`; the extension raises that layer above the content so opaque
+token backgrounds cannot cover them, and leaves it transparent to touch.
+The handle dots extend 8px past their range; matching scroller padding and
+negative margin expand the clip area without moving the text or changing the
+composer height. iOS still paints its taller system selection overlay even
+when CSS makes `::selection` transparent. The extension therefore suppresses
+CodeMirror's synthetic selection rectangles on iOS while leaving its handles,
+cursor path and `nativeSelectionHidden` facet active. Otherwise the grey system
+highlight and themed rectangle overlap with visibly different heights.
+Do not add a second custom layer or custom handles here: overlapping translucent
+rectangles make selection darker at their seams and imitated handles drift from
+the geometry WebKit actually manipulates. What iOS avoids is installing the
+native-selection workaround above: explicitly restoring native paint and caret
+makes WebKit re-measure them after every decoration redraw, and the composer
+rebuilds every decoration on every keystroke. That cost is felt worst during
+IME composition.
+
+The non-iOS native selection tint comes from `--primary`, not the selection
+token: themes define `--interactive-selection` with its own alpha, so mixing it
+with transparent again is nearly invisible. The iOS system overlay owns its
+visible selection fill.
+
+The content element keeps the existing correction policy: on in the mobile UI,
+off elsewhere. CodeMirror also reads the attribute and reverts Apple and
+Android's insert-period-on-double-space only when its value is exactly `off`.
+`editor/autocorrect.ts` uses the HTML standard's
+[ASCII case-insensitive `autocorrect` keywords](https://html.spec.whatwg.org/multipage/interaction.html#attr-autocorrect)
+to keep desktop word correction off while avoiding that CodeMirror-only
+revert. Its platform checks deliberately match CodeMirror's own browser flags.
 
 `composerLanguage.ts` retokenizes the whole document on every change. The
 composer holds a prompt, not a source file: it is short enough that a full pass
@@ -100,10 +153,14 @@ and the send path reading the same grammar.
   drawn caret through a class it only writes while applying an update, so the
   selection has to be the update that follows the focus.
 - `submit/buildOutgoingMessage.ts` flattens queued messages, the composer text,
-  inline comments and context into OpenCode's one-primary-plus-parts shape. The
-  oldest queued message becomes primary; **inline comments attach to the last
-  body the user authored** rather than becoming their own part; PR instructions
-  precede the PR diff.
+  context drafts and linked references into OpenCode's one-primary-plus-parts
+  shape. The oldest queued message becomes primary. **Every attached context
+  item (inline comments, terminal selections, browser annotations, PR context,
+  linked issue/PR) becomes its own synthetic text part carrying structured
+  metadata** built by `lib/messages/contextParts.ts`; the timeline reads that
+  metadata back to render context blocks. PR instructions precede the PR diff.
+  Queueing a message leaves context drafts in their store on purpose — the send
+  that later delivers the queue consumes them.
 - `state/useComposerDraft.ts` — a draft belongs to a (runtime, directory,
   session) identity. Writes are debounced while typing but forced at every edge
   where the page may stop running, because a pending timer is not a saved
@@ -113,6 +170,9 @@ and the send path reading the same grammar.
 - `state/useDraftTarget.ts` — the draft can target a directory that does not
   exist yet (a worktree being created). It must survive not appearing in the
   branch list, or the selector snaps back to the project root mid-creation.
+- `ui/DraftTargetSelectors.tsx` owns the controlled project/worktree picker
+  state and registers its application shortcuts locally. The selectors only
+  consume their shared prefix while the draft target UI is mounted.
 
 ## Mobile