docs: capsite AGENTS.md for agent working rules

The hard rules move from the goal tree into a proper AGENTS.md at the
capsite root (discoverable by agents without reading the tree; the
workspace AGENTS.md's commit-trailer policy stays where it is, linked).
Checklist keeps a one-line pointer, so a continuation prompt still
surfaces them. Error hygiene (no header/param values in messages)
groups with secrets discipline there rather than as its own rule.

Generated-by: opencode (GLM)

AGENTS.md

@@ -0,0 +1,28 @@
+# capsite working rules
+
+Applies to AI agents working in `capsite/` (goal tree + how-to-run:
+[capsite-checklist.md](capsite-checklist.md); background:
+[the capsite notes](capsite-notes.md); workspace-wide policy:
+[AGENTS.md](../AGENTS.md) — commit trailers live there).
+
+## Dev servers are the user's job
+
+The assistant never starts, stops, or restarts long-running dev servers
+(`wrangler dev`, `pnpm dev`/`astro dev`). The user runs them and owns the
+terminals; the assistant observes via `.tmp/capsite.script` (the `script`
+capture; use `watchme`). One-shot codegen (`wrangler types`), linters,
+typechecks, and tests are fine.
+
+## Secrets discipline
+
+Worker secrets never in source or wrangler config. `.dev.vars` (gitignored)
+locally; `wrangler secret put` deployed. As of the DO split, the cookie
+lives only in the webapp DO's storage; `DIIGO_WEB_ID` is the one
+diigo-dump secret. Error messages must not contain header or param values
+(they cross RPC as exceptions and land in logs); URLs appear query-stripped.
+
+## Keep config types generated
+
+Run `wrangler types` after any wrangler.jsonc change
+(`worker-configuration.d.ts` is generated, gitignored; hand-rolled
+`cloudflare:workers` shims drift and gave red squiggles).