practice: resolveTargetId + ids-first context marker (round 9 slice 1)

The mastery-trace contract: problem targets must be traceable to
propositions. resolveTargetId (pure, chains.ts) resolves a target
string to a canonical node id — id exact first, then name
case-insensitive — against the WHOLE graph (pickless sessions and
future graph-tools poses stay valid). The graph-context marker now
introduces each pick as [id] name: statement (ids were never shown to
the model before — names only); chains stay names: comprehension
context, not tags.

src/core/chains.ts

@@ -1,3 +1,5 @@
+import type { GraphNode } from "./contracts/graph.ts";
+
 /**
  * Selection-facing chain views — pure + browser-safe (the shell's chain
  * table consumes these; the barrel exports them). Born in the practice
@@ -55,6 +57,27 @@ export function chainsForSelection(
  *  singleton shows its "(no premises)" marker. Pure + browser-safe.
  *  Unknown ids fall back to the raw id (honest, never guessed).
  *  Premises sort by id — the same determinism law as chainsForSelection. */
+/** Resolve ONE target string to a canonical proposition id (owner round
+ *  9, 2026-10-05 — the mastery-trace contract): id first (exact), then
+ *  name (case-insensitive, trimmed — names are presentational handles,
+ *  not unique; an ambiguous name resolves to the FIRST node in store
+ *  order). Returns null when nothing matches — the caller rejects.
+ *  Validation set is the WHOLE graph, not the session's picks: pickless
+ *  sessions and future graph-tools poses stay valid. */
+export function resolveTargetId(
+	target: string,
+	nodes: ReadonlyArray<Pick<GraphNode, "id" | "name">>,
+): string | null {
+	const t = target.trim();
+	if (t.length === 0) return null;
+	if (nodes.some((n) => n.id === t)) return t;
+	const lower = t.toLowerCase();
+	for (const n of nodes) {
+		if (n.name.trim().toLowerCase() === lower) return n.id;
+	}
+	return null;
+}
+
 export function formatChainLine(
 	chain: Pick<ReasoningChain, "premises" | "conclusion">,
 	propositions: Readonly<Record<string, { name: string }>>,

src/core/native-messages.ts

@@ -203,11 +203,16 @@ export interface GraphContextPick {
  *  feeds the transcript's collapsible GraphContextCard. No more seed
  *  text glued into the first prompt. */
 export function newGraphContextMessage(picks: readonly GraphContextPick[], chains: readonly string[]): LhMarkerMessage {
+	// IDS FIRST (owner round 9, 2026-10-05 — the mastery-trace contract):
+	// each proposition is introduced ONCE with its id, name, and statement;
+	// the problem tool's `target` field takes these ids (names normalize to
+	// ids at the seam). Chains below stay NAMES — they are comprehension
+	// context, not tags; names read, ids reference.
 	const lines = [
 		"Contextualization — the learner picked these propositions from their knowledge map when starting this session:",
 		"",
-		"Propositions:",
-		...picks.map((p) => `- ${p.name}: ${p.statement}`),
+		"Propositions (id — name: statement; the problem tool's target field uses these ids):",
+		...picks.map((p) => `- [${p.id}] ${p.name}: ${p.statement}`),
 	];
 	if (chains.length > 0) {
 		lines.push("", "Reasoning chains among them (premises → conclusion):", ...chains.map((c) => `- ${c}`));