practice UI: the dock, the transcript cards, layered-Esc discard

- PracticeDock (components/practice-dock.tsx): the active problem
  replaces the composer — statement (markdown+LaTeX) above, the 'Your
  thinking' composer-twin below with the two submit lanes (Nudge =
  thinking without a commit; Commit = answer commit; ⌘/Ctrl+Enter
  commits). Dictation claims the thinking field.
- Transcript cards (practice-cards.tsx + the artifact registry): the
  problem card (compact-expandable statement — the commitment NEVER
  renders), the conclude card (outcome + verdict + reveal; the
  dismissal synthesis is one muted line), and the user-side thinking
  register cards (Your thinking / Your solution).
- view.ts: the problem pose joins the placeholder fork (the ack never
  flips the part); practice-thinking markers project as data parts;
  problem-dismissed markers project nothing.
- chat.tsx: activeProblemOf drives the dock branch (question > problem
  > composer), the esc layering gains the problem rung (below question,
  above turn) with its discard confirm + the silent marker route; the
  thinking submissions POST through the session's optimistic appends.

components/artifacts/index.ts

@@ -5,6 +5,7 @@ import { JobCard, PdfJobCard } from "@/components/artifacts/job-card";
 import { VisualCard } from "@/components/artifacts/visual-card";
 import { ProbeDoneCard } from "@/components/artifacts/probe-done-card";
 import { ToolCallCard } from "@/components/artifacts/tool-call-card";
+import { ProblemCard, ConcludeCard } from "@/components/practice-cards";
 
 /**
  * Artifact renderer registry — the extension point for tool-part UI.
@@ -37,6 +38,11 @@ export const artifactRenderers: Record<string, ComponentType<ArtifactPartProps>>
 	ls: ToolCallCard,
 	find: ToolCallCard,
 	grep: ToolCallCard,
+	// The practice pair (2026-10-04): the pose renders the statement ONLY
+	// (the commitment lives in the call's arguments and never renders);
+	// the conclusion carries the outcome + verdict + the reveal.
+	problem: ProblemCard,
+	conclude: ConcludeCard,
 	// The prober's graph tools (wave 7): same quiet expandable card —
 	// collapsed one-liner (tool name + the session id for
 	// list_propositions), the tool's own compact row-per-line output