automc: pg LISTEN/NOTIFY route source + HTTP waker

Adds opt-in extension package internal/automc/ that:
- Subscribes to Postgres notifications on a 'servers' table and pushes
  route changes into server.Routes (no file I/O, no fsnotify).
- Provides a WakerFunc that POSTs to a configurable HTTP control plane
  (server-manager) and polls until state=running.

When AUTOMC_DSN is unset, Wire() is a no-op and the binary behaves
exactly like upstream itzg/mc-router. Single patch site in main.go
(import + 4-line call) keeps upstream rebases trivial.

See docs/AUTOMC.md for env vars and the expected DB schema/trigger.

docs/AUTOMC.md

@@ -0,0 +1,85 @@
+# automc extensions
+
+Soft fork of `itzg/mc-router` that adds Postgres-driven route management and an HTTP waker, without touching upstream behavior by default.
+
+The `internal/automc` package is opt-in via env vars: with `AUTOMC_DSN` unset, the binary behaves exactly like upstream.
+
+## Environment variables
+
+| Var | Required | Purpose |
+|---|---|---|
+| `AUTOMC_DSN` | yes (to enable) | Postgres DSN, e.g. `postgres://user:pass@host:5432/automc?sslmode=disable`. When unset, automc is a no-op. |
+| `AUTOMC_WAKER_URL` | no | Base URL of the waker control plane (server-manager). When set, stopped backends are auto-started on login. |
+| `AUTOMC_WAKER_TOKEN` | no | Sent as `X-API-Key` header on every waker request. |
+
+Recommended companion upstream flags:
+
+- `--use-asleep-motd` / `--use-loading-motd` — supplies friendly MOTD to clients during the wake window. Already implemented upstream; automc does not duplicate this.
+
+## Postgres schema
+
+Apply this once to the database referenced by `AUTOMC_DSN`. mc-router only reads; the trigger is what tells it to re-read.
+
+```sql
+CREATE TABLE IF NOT EXISTS servers (
+    name    TEXT PRIMARY KEY,
+    domain  TEXT NOT NULL,
+    address TEXT NOT NULL,
+    state   TEXT NOT NULL DEFAULT 'stopped',
+    UNIQUE(domain)
+);
+
+CREATE OR REPLACE FUNCTION automc_notify_routes_changed() RETURNS trigger AS $$
+BEGIN
+    PERFORM pg_notify('automc_routes_changed', '');
+    RETURN NULL;
+END;
+$$ LANGUAGE plpgsql;
+
+DROP TRIGGER IF EXISTS automc_servers_route_notify ON servers;
+CREATE TRIGGER automc_servers_route_notify
+    AFTER INSERT OR UPDATE OF domain, address, state OR DELETE ON servers
+    FOR EACH ROW EXECUTE FUNCTION automc_notify_routes_changed();
+```
+
+The trigger fires on every mutation to a route-relevant column. mc-router holds a persistent `LISTEN automc_routes_changed` and re-runs `SELECT name, domain, address FROM servers WHERE domain != '' AND address != ''`, diffing against its in-memory map. Adds/removes/changes call `server.Routes.CreateMapping` and `DeleteMapping` directly — no file I/O.
+
+State column is not read by mc-router; it exists to drive the trigger and for the waker's own ready-check.
+
+## Waker contract
+
+When `AUTOMC_WAKER_URL` is set, every route is registered with a `WakerFunc` that the upstream connector calls only when a client tries to LOGIN (not on status pings — those are answered locally via `--use-asleep-motd`).
+
+The waker:
+
+1. `POST {AUTOMC_WAKER_URL}/servers/{name}/start` — fire-and-forget start signal. `409 Conflict` is treated as success (already starting).
+2. Polls `GET {AUTOMC_WAKER_URL}/servers/{name}` every 2 s, expecting JSON `{"state":"running","address":"host:port"}`.
+3. Returns the polled `address` once `state == "running"`, or errors after 90 s.
+
+The polled address overrides the route's static address for that connection only — useful when the backend's IP is allocated lazily.
+
+## Upstream sync
+
+```
+make sync-upstream
+```
+
+Fetches `upstream/main`, rebases the `automc` branch onto it, builds, and runs the automc tests. The patch surface is intentionally tiny so rebase conflicts are rare:
+
+```
+cmd/mc-router/main.go  — 1 import line + 4-line Wire call
+internal/automc/       — new directory; no upstream conflicts possible
+docs/AUTOMC.md         — new doc; no upstream conflicts
+Makefile               — appended targets only
+go.mod / go.sum        — pgx dep added; mergeable
+```
+
+If upstream renames `server.Routes.CreateMapping` or changes its signature, only `pgsync.go:apply` needs adjustment.
+
+## Verification
+
+```
+go build ./...
+go test ./internal/automc/...
+go vet ./...
+```