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.

components/graph-context-control.tsx

@@ -0,0 +1,67 @@
+"use client";
+
+import { BookOpenIcon } from "lucide-react";
+import {
+	GRAPH_CONTEXT_TOKENS_DEFAULT,
+	GRAPH_CONTEXT_TOKENS_MAX,
+	GRAPH_CONTEXT_TOKENS_STEP,
+} from "@/src/core";
+import { formatTokens } from "@/components/usage-format";
+
+/**
+ * The knowledge-context budget control (vision-context-injection.md) — the
+ * "session data" section's one input, shown where sessions START: the home
+ * (graph) view's new-session dock and the /chat/new draft. Input before
+ * output: the panel that will later show what the session contributed to
+ * the graph asks first what the graph will contribute to the session.
+ *
+ * One quiet slider row: the token budget for the prior-knowledge block the
+ * injection steers in at session start. 0 = off; absent settings show the
+ * DEFAULT (1024 — on). The value rides ChatSettings (the same lifted
+ * settings the model picker uses), so it persists pre-chat via the same
+ * deferred PUT. Sessions never show this control — the injection is
+ * one-shot at session start, so mid-session there is nothing to decide.
+ */
+export function GraphContextControl({
+	value,
+	onChange,
+	testId = "graph-context-control",
+}: {
+	value: number;
+	onChange: (tokens: number) => void;
+	testId?: string;
+}) {
+	return (
+		<div
+			data-testid={testId}
+			className="flex items-center gap-2 px-1 text-xxs text-muted-foreground"
+		>
+			<BookOpenIcon className="size-3 shrink-0" />
+			<span className="shrink-0 uppercase tracking-widest">Knowledge context</span>
+			<input
+				type="range"
+				min={0}
+				max={GRAPH_CONTEXT_TOKENS_MAX}
+				step={GRAPH_CONTEXT_TOKENS_STEP}
+				value={value}
+				onChange={(e) => onChange(Number(e.target.value))}
+				aria-label="Prior-knowledge token budget"
+				className="h-1 flex-1 accent-primary"
+				data-testid="graph-context-slider"
+			/>
+			<span
+				className="w-16 shrink-0 text-right tabular-nums"
+				data-testid="graph-context-value"
+			>
+				{value === 0 ? "off" : `${formatTokens(value)} tokens`}
+			</span>
+		</div>
+	);
+}
+
+/** The control's effective value for a chat's settings — absent = the
+ *  default (on), never 0: the decided default is a modest slice of prior
+ *  knowledge for every fresh session. */
+export function effectiveContextTokens(settings: { graphContextTokens?: number } | undefined): number {
+	return settings?.graphContextTokens ?? GRAPH_CONTEXT_TOKENS_DEFAULT;
+}