feat: add wiki-compile-nudge workflow + document it

Daily Google Chat nudge when wiki-vault is due for a compile (>=10 new
sources or >=7 days stale). Drift query against petalbrain; needs a
wiki.compile_runs table + post-import credential/webhook wiring.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -47,6 +47,29 @@ Rotate any of these by editing `.env` and restarting:
 If you need a checked-in template, create `.env.example` with the keys
 but no values.
 
+## Workflows (version-controlled here)
+
+Importable workflow JSON lives in `workflows/`. The live workflows are
+stored in the n8n volume; these files are the reviewable, git-tracked
+source. Import via the UI (Workflows → Import from File) or
+`POST /api/v1/workflows` with an `X-N8N-API-KEY` header.
+
+| File                              | Purpose                                                        |
+|-----------------------------------|----------------------------------------------------------------|
+| `workflows/wiki-compile-nudge.json` | Daily check that nudges Google Chat when the wiki-vault is due for a compile (≥10 new sources, or ≥7 days stale). Schedule → Postgres drift query against `petalbrain` → IF → Google Chat HTTP POST. |
+
+**`wiki-compile-nudge` — before it runs:**
+
+- Fill two placeholders after import: the **Postgres credential** (select
+  the existing `petalbrain` cred) and the **Google Chat space webhook URL**
+  in the HTTP node.
+- Depends on a `wiki.compile_runs` table in `petalbrain`
+  (`id bigserial`, `compiled_at timestamptz default now()`) and the
+  wiki-maintenance compile writing a row to it on each run — the drift
+  query reads `max(compiled_at)` as its "last compile" baseline.
+- The drift logic is in SQL (returns a `should_notify` boolean), so the
+  IF node just checks that flag.
+
 ## Persistence — external volume
 
 ```

workflows/wiki-compile-nudge.json

@@ -0,0 +1,85 @@
+{
+  "name": "wiki-compile-nudge",
+  "nodes": [
+    {
+      "parameters": {
+        "rule": {
+          "interval": [
+            { "field": "cronExpression", "expression": "7 20 * * *" }
+          ]
+        }
+      },
+      "id": "schedule-trigger",
+      "name": "Daily @ 20:07",
+      "type": "n8n-nodes-base.scheduleTrigger",
+      "typeVersion": 1.2,
+      "position": [260, 300]
+    },
+    {
+      "parameters": {
+        "operation": "executeQuery",
+        "query": "WITH last AS (\n  SELECT COALESCE(max(compiled_at), 'epoch') AS ts FROM wiki.compile_runs\n),\nn AS (\n  SELECT count(*) AS c FROM wiki.artifacts WHERE created_at > (SELECT ts FROM last)\n)\nSELECT\n  (SELECT c FROM n)                                                       AS new_sources,\n  EXTRACT(day FROM now() - (SELECT ts FROM last))::int                    AS days_since,\n  (\n    (SELECT c FROM n) >= 10\n    OR (EXTRACT(day FROM now() - (SELECT ts FROM last)) >= 7 AND (SELECT c FROM n) >= 1)\n  )                                                                       AS should_notify;",
+        "options": {}
+      },
+      "id": "postgres-drift",
+      "name": "Drift query (petalbrain)",
+      "type": "n8n-nodes-base.postgres",
+      "typeVersion": 2.5,
+      "position": [480, 300],
+      "credentials": {
+        "postgres": { "id": "REPLACE_WITH_PETALBRAIN_CRED_ID", "name": "Petalbrain Postgres" }
+      }
+    },
+    {
+      "parameters": {
+        "conditions": {
+          "options": { "caseSensitive": true, "typeValidation": "strict", "version": 2 },
+          "combinator": "and",
+          "conditions": [
+            {
+              "leftValue": "={{ $json.should_notify }}",
+              "rightValue": true,
+              "operator": { "type": "boolean", "operation": "true", "singleValue": true }
+            }
+          ]
+        },
+        "options": {}
+      },
+      "id": "if-should-notify",
+      "name": "Compile due?",
+      "type": "n8n-nodes-base.if",
+      "typeVersion": 2,
+      "position": [700, 300]
+    },
+    {
+      "parameters": {
+        "method": "POST",
+        "url": "REPLACE_WITH_GOOGLE_CHAT_SPACE_WEBHOOK_URL",
+        "sendBody": true,
+        "specifyBody": "json",
+        "jsonBody": "={\n  \"text\": \"\\ud83c\\udf3f Wiki compile due \\u2014 {{ $json.new_sources }} new sources, {{ $json.days_since }}d since last compile.\\nRun: \\\"compile the wiki at /opt/projects/wiki-vault\\\"\"\n}",
+        "options": {}
+      },
+      "id": "google-chat-notify",
+      "name": "Google Chat nudge",
+      "type": "n8n-nodes-base.httpRequest",
+      "typeVersion": 4.2,
+      "position": [920, 220]
+    }
+  ],
+  "connections": {
+    "Daily @ 20:07": {
+      "main": [[{ "node": "Drift query (petalbrain)", "type": "main", "index": 0 }]]
+    },
+    "Drift query (petalbrain)": {
+      "main": [[{ "node": "Compile due?", "type": "main", "index": 0 }]]
+    },
+    "Compile due?": {
+      "main": [
+        [{ "node": "Google Chat nudge", "type": "main", "index": 0 }],
+        []
+      ]
+    }
+  },
+  "settings": { "executionOrder": "v1" }
+}