feat: graph context injection — the session's prior knowledge, steered in at session start (vision-context-injection.md)

One shot per chat, fired at the first turn's onFinish: the session's
topic (its only typed message) is embedded as an EmbeddingGemma retrieval
query; the semantically closest graph propositions are selected under the
session's token budget (pure budget, no similarity threshold — the
decided doctrine) and delivered as a marker-only steer through the wake
pipeline, queuing behind pending questions like every sub-agent result.

- contracts: ChatSettings.graphContextTokens (default 1024, max 4096,
  step 128, 0 = off); GraphContextData + graphContextText; the
  graph-context JobKind + buildGraphContextSteer (id steer_ctx_<chatId>)
- core/graph-context.ts: brute-force cosine top-K, greedy chars/4 fill
  under budget, most-recent UnderstandingLevel fold, count cap 64,
  parse-don't-cast at the marker seam
- server: embedQuery (role-asymmetric query format, same warm singleton
  — vector-space parity by construction); the runner (startGraphContext-
  Injection one-shot gates; runGraphContextJob validates ledger parity);
  wake branches (chatIdOf/jobIdOf, finalizeJob done, recoverStaleJobs
  re-deliver or contextRespawn); abortJob kills context jobs SILENTLY
  (nothing was promised in the lesson); turn-service trigger seam
- adapter: data-graph-context flattens to the canonical block (malformed
  parts have no model face)
- UI: the budget slider (home dock + /chat/new draft, the session-data
  strip); the quiet SystemLine "~537 · 10 propositions"; dock kind
  "Knowledge context"; model-picker PUT now spreads settings (a model
  pick can no longer clear the sibling override)

Live-smoked end to end on the real embedder + real GLM: seeded ledger
(10 propositions), session on "modal logic: possible worlds and the
necessity box" — job in the dock, queued behind the prober's question,
delivered on the answer, SystemLine in the transcript, wake turn reads
the block and continues the probe. Gates: tsc, lint, 459/459, build.

src/core/ui-message.ts

@@ -1,6 +1,7 @@
 import type { UIMessage } from "ai";
 import type {
 	DemoToolInput,
+	GraphContextData,
 	PlanVerdictData,
 	PlanBlockData,
 	ProbeDoneInput,
@@ -46,6 +47,10 @@ export type TeacherUIDataParts = {
 	/** The probe→teach handoff wake: the wake pipeline's steer message,
 	 *  carrying ONLY this part (the model-facing text lives in the adapter). */
 	"probe-handoff": { chatId: string };
+	/** The prior-knowledge injection's delivery (vision-context-injection.md):
+	 *  the marker-only steer — the counts for the UI, the full block content
+	 *  for the audit trail; the adapter flattens it to graphContextText. */
+	"graph-context": GraphContextData;
 	/** The abort steer's message-type marker (the abort badge renders off it). */
 	"subagent-aborted": SubagentResultMeta & { aborted: true };
 };