feat(core): make path-local instruction discovery durable

Replace synthetic-message instruction injection with a durable
discovery projection so discovered AGENTS.md files survive compaction,
forks, reverts, and restarts.

- Add the instruction_file table and the durable
  session.instructions.discovered event; projection stores each
  discovered path and content with its owning assistant-message
  boundary and durable discovery order.
- Fold discovered files into the core/instructions source through
  InstructionDiscovery, absorbing SessionInstructions. Completed
  compaction rebaselines restate discovered instructions instead of
  summarizing them away.
- Re-read discovered files live at each observation so mid-session
  edits reach the model; the frozen discovery content stands in only
  when a file becomes unreadable.
- Narrate instruction file changes as per-file deltas via diffByKey,
  restating the full set only for pure reorderings.
- Fork copies discoveries within the inherited transcript, committed
  revert removes discoveries past the revert boundary, and Session
  movement clears them so the destination initializes a complete
  baseline.

packages/client/src/promise/generated/types.ts

@@ -1222,6 +1222,20 @@ export type SessionLogOutput =
           readonly location?: { readonly directory: string; readonly workspaceID?: string }
           readonly data: { readonly sessionID: string; readonly text: string }
         }
+      | {
+          readonly id: string
+          readonly created: number
+          readonly metadata?: { readonly [x: string]: unknown }
+          readonly type: "session.instructions.discovered"
+          readonly durable: { readonly aggregateID: string; readonly seq: number; readonly version: number }
+          readonly location?: { readonly directory: string; readonly workspaceID?: string }
+          readonly data: {
+            readonly sessionID: string
+            readonly assistantMessageID: string
+            readonly location: { readonly directory: string; readonly workspaceID?: string }
+            readonly files: ReadonlyArray<{ readonly path: string; readonly content: string }>
+          }
+        }
       | {
           readonly id: string
           readonly created: number
@@ -4473,6 +4487,20 @@ export type EventSubscribeOutput =
       readonly location?: { readonly directory: string; readonly workspaceID?: string }
       readonly data: { readonly sessionID: string; readonly text: string }
     }
+  | {
+      readonly id: string
+      readonly created: number
+      readonly metadata?: { readonly [x: string]: unknown }
+      readonly type: "session.instructions.discovered"
+      readonly durable: { readonly aggregateID: string; readonly seq: number; readonly version: number }
+      readonly location?: { readonly directory: string; readonly workspaceID?: string }
+      readonly data: {
+        readonly sessionID: string
+        readonly assistantMessageID: string
+        readonly location: { readonly directory: string; readonly workspaceID?: string }
+        readonly files: ReadonlyArray<{ readonly path: string; readonly content: string }>
+      }
+    }
   | {
       readonly id: string
       readonly created: number