Storage ports: ChatStore/GraphStore/JobStore + adapters + core inversion (stage 3)

Per-entity semantic ports (src/core/ports.ts), one adapter family
(src/store/*, fs JSON/JSONL), exactly one composition point
(src/server/stores.ts). Dependency direction is now machine-checked:
adapters implement core interfaces; core never imports an adapter.

The inversion:
- core/graph.ts (emitChat/getGraph/graphSnapshot/foldStaleChats) is now
  pure — it takes the storage ports as explicit parameters (GraphDeps).
  No store imports; newGraphNodeId is local; node id format unchanged.
- core/graph-context.ts buildGraphContext() no longer defaults to the
  live ledgers: the chat-handler hands in getGraph(graphStore) per turn.
- store adapters export exactly one object each implementing their port
  (chatStore/graphStore/jobStore); bodies otherwise verbatim.
  NodeMapping + SessionCheckpoint moved store/graph -> core/contracts
  (they ARE contract shapes); CreateJobInit/JobPatch live in ports.
- titleFromPrompt moved store/chats -> core/contracts (pure helper,
  planNodeStatus precedent). Store modules now contain persistence only.
- server/stores.ts is the composition root; server/{chats,graph,jobs}.ts
  and chat-handler wire from it; agent (plan tools, sub-agent runner)
  call the port objects. The shell surface (@/src/server exports) is
  unchanged.

Lint law extended: the whole of src/core is now a purity zone (was a
file glob with a graph/graph-context exemption). Verified it fires on
core->store imports; tsc clean, 190/190 tests, eslint clean, prod build
clean (prerender 6/6). Tests pass deps explicitly — graph.test uses the
same fs-adapter pair stores.ts wires in production; graph-context.test
keeps its in-memory ledgers as a GraphStore implementation.

eslint.config.mjs

@@ -10,7 +10,8 @@ import importPlugin from "eslint-plugin-import";
  *
  *   components/**  →  "@/src/core"  (the pure core barrel) — ONLY
  *   app/**         →  "@/src/core" + "@/src/server" (the server barrel) — ONLY
- *   pure core      →  never imports src/agent, src/server, src/store
+ *   src/core/**    →  never imports src/agent, src/server, src/store (pure
+ *                    core: adapters implement core/ports.ts, never the reverse)
  *
  * tests/ and scripts/ are internal — unrestricted.
  */
@@ -49,10 +50,10 @@ export default defineConfig([
 								"app/ (transport + server components) imports ONLY the barrels: `@/src/core` and `@/src/server` (architecture: docs/architecture.md).",
 						},
 						{
-							target: "./src/core/{index,contracts,question-core,plan-tree,phases,pending,math-delims,ui-message}.ts",
+							target: "./src/core",
 							from: ["./src/agent", "./src/server", "./src/store"],
 							message:
-								"Pure core modules never import IO layers (agent/server/store). IO-bound core (graph.ts, graph-context.ts) is exempt until the storage-port stage inverts it.",
+								"Pure core never imports IO layers (agent/server/store): adapters implement core/ports.ts, and the composition root (src/server/stores.ts) passes them in (architecture: docs/architecture.md).",
 						},
 					],
 				},