feat(T2b): sources v0 — read tool + pdf-reader sub-agent

Learner source files, on the teacher's own terms (nothing auto-injects):

- read tool (src/agent/tools/read.ts): pi-read port — path/offset/limit,
  2000-line/50KB truncation with use-offset continuation notices, image
  files (jpg/png/gif/webp/bmp) returned as native image content parts
  (new LhToolImageResult escape hatch in lh-tool.ts). Always-on in both
  the prober and teacher registries (user-decided 2026-09).
- pdf-reader sub-agent (JobKind 'pdf', toggleable, ack-and-steer): triage
  via pdf_info (pdfjs text layer: per-page text/image/math-density),
  targeted pdf_extract, regex pdf_search (hits count as consultation),
  and pdf_render — pages painted by pdfjs onto a canvas shim in headless
  Chrome (the pdfium viewer doesn't paint headless), screenshot fed back
  image-in-the-loop (visual-maker idiom, providerSafePng applied). The
  unread-finish gate bounces a zero-consultation brief once. Teacher gets
  a text brief with page citations only; renders never leave the loop.
- MODELS.pdfReader = qwen/qwen3.8-flash (user override 2026-09-19: the
  look-at-renders workload wants the vision-proven model; catalog listed
  glm-5.3-flash as image-capable but qwen is the known-good daily driver).
- UI: PdfCompleteBadge + PdfBriefCard (steer-card, job-card), dispatch
  card + activity-dock kind entries (type-forced, flagged for UI review).
- Prompts: 'Learner source files' section in teacher/30-jobs.md; read
  line in prober/10-probe-doctrine.md. Doctrine rides tool descriptions
  per the self-contained-tools principle.

src/agent/tools/jobs.ts

@@ -21,7 +21,7 @@ export interface JobToolContext {
 	/** Fire the background runner for a fresh job — fire-and-forget. The
 	 *  input rides along because the spawn happens MID-STREAM, before
 	 *  onFinish persists the tool part — a transcript scan would race it. */
-	spawn: (job: JobRecord, input: ResearchInput | DemoInput | VisualInput) => void;
+	spawn: (job: JobRecord, input: ResearchInput | DemoInput | VisualInput | PdfInput) => void;
 }
 
 export const researchInputSchema = z.object({
@@ -53,6 +53,16 @@ export const visualInputSchema = z.object({
 		),
 });
 
+export const pdfInputSchema = z.object({
+	path: z.string().describe("Path to the learner's PDF (relative or absolute), exactly as they gave it."),
+	question: z
+		.string()
+		.describe(
+			"What you need from the document — the specific content, explanation, or answer to extract and brief. " +
+			"The reader sees NOTHING else of the lesson.",
+		),
+});
+
 /**
  * The per-call dispatch: create the job (idempotent by toolCallId), fire the
  * runner, and return the ack. Shared by all three tools — only kind differs.
@@ -62,7 +72,7 @@ function dispatch(
 	kind: JobRecord["kind"],
 	toolCallId: string,
 	ack: string,
-	input: ResearchInput | DemoInput | VisualInput,
+	input: ResearchInput | DemoInput | VisualInput | PdfInput,
 ): string {
 	const existing = ctx.jobStore.findJobByToolCallId(ctx.chatId, toolCallId);
 	const job = existing ?? ctx.jobStore.createJob({ kind, chatId: ctx.chatId, toolCallId });
@@ -79,6 +89,9 @@ const DEMO_ACK =
 const VISUAL_ACK =
 	"This call is fire-and-forget: continue your turn and keep teaching — do not wait, poll, or mention waiting. " +
 	"The verified figure arrives as a new message when ready and is rendered in the lesson; reference it then.";
+const PDF_ACK =
+	"This call is fire-and-forget: continue your turn and keep teaching — do not wait, poll, or mention waiting. " +
+	"The document brief arrives as a new message when ready; weave it into the lesson and cite its pages.";
 
 const RESEARCH_DESCRIPTION =
 	"Dispatch a background web-research agent: fact verification, current data, or niche specifics you are not certain about. " +
@@ -97,6 +110,12 @@ const VISUAL_DESCRIPTION =
 	"function plots, physical layouts. For flows/relations/taxonomies write mermaid inline instead. " +
 	"The call is ASYNC and fire-and-forget — it resolves immediately and your turn continues; the verified figure arrives later " +
 	"as a new message.";
+const PDF_DESCRIPTION =
+	"Dispatch a background sub-agent that READS a learner-provided PDF on your behalf (triage, targeted extraction, visual page " +
+	"reading for equations and diagrams) and returns a brief with page citations. Use it when the learner gives you a PDF path " +
+	"and you need its CONTENT for the lesson. The call is ASYNC and fire-and-forget — it resolves immediately and your turn " +
+	"continues; the brief arrives later as a new message. For quick looks at plain text or image files, use the read tool " +
+	"directly instead of dispatching.";
 
 /**
  * Per-request job tool registry: each tool closes over the composition root's
@@ -123,9 +142,16 @@ export function jobTools(ctx: JobToolContext): Record<string, LhTool<any, any>>
 			schema: visualInputSchema,
 			execute: async (input, { toolCallId }) => dispatch(ctx, "visual", toolCallId, VISUAL_ACK, input),
 		}),
+		pdf: lhTool({
+			name: "pdf",
+			description: PDF_DESCRIPTION,
+			schema: pdfInputSchema,
+			execute: async (input, { toolCallId }) => dispatch(ctx, "pdf", toolCallId, PDF_ACK, input),
+		}),
 	};
 }
 
 export type ResearchInput = z.infer<typeof researchInputSchema>;
 export type DemoInput = z.infer<typeof demoInputSchema>;
 export type VisualInput = z.infer<typeof visualInputSchema>;
+export type PdfInput = z.infer<typeof pdfInputSchema>;