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/core/schema.json

@@ -1,9 +1,9 @@
 {
   "version": "7",
   "dialect": "sqlite",
-  "id": "992b24b9-f3e9-41f5-87a5-4917d1423169",
+  "id": "4689ab8e-76e3-429e-832c-403de6b7de57",
   "prevIds": [
-    "96e9fe64-660f-4a73-9414-b38bb7eac290"
+    "992b24b9-f3e9-41f5-87a5-4917d1423169"
   ],
   "ddl": [
     {
@@ -58,6 +58,10 @@
       "name": "instruction_entry",
       "entityType": "tables"
     },
+    {
+      "name": "instruction_file",
+      "entityType": "tables"
+    },
     {
       "name": "message",
       "entityType": "tables"
@@ -876,6 +880,66 @@
       "entityType": "columns",
       "table": "instruction_entry"
     },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "session_id",
+      "entityType": "columns",
+      "table": "instruction_file"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "path",
+      "entityType": "columns",
+      "table": "instruction_file"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "content",
+      "entityType": "columns",
+      "table": "instruction_file"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "message_seq",
+      "entityType": "columns",
+      "table": "instruction_file"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "discovered_seq",
+      "entityType": "columns",
+      "table": "instruction_file"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "position",
+      "entityType": "columns",
+      "table": "instruction_file"
+    },
     {
       "type": "text",
       "notNull": false,
@@ -1651,6 +1715,21 @@
       "entityType": "fks",
       "table": "instruction_entry"
     },
+    {
+      "columns": [
+        "session_id"
+      ],
+      "tableTo": "session",
+      "columnsTo": [
+        "id"
+      ],
+      "onUpdate": "NO ACTION",
+      "onDelete": "CASCADE",
+      "nameExplicit": false,
+      "name": "fk_instruction_file_session_id_session_id_fk",
+      "entityType": "fks",
+      "table": "instruction_file"
+    },
     {
       "columns": [
         "session_id"
@@ -1786,6 +1865,16 @@
       "entityType": "pks",
       "table": "instruction_entry"
     },
+    {
+      "columns": [
+        "session_id",
+        "path"
+      ],
+      "nameExplicit": false,
+      "name": "instruction_file_pk",
+      "entityType": "pks",
+      "table": "instruction_file"
+    },
     {
       "columns": [
         "session_id",
@@ -2252,4 +2341,4 @@
     }
   ],
   "renames": []
-}
+}