feeders: stage beside the palace, not in ~/.cache; document Phase 1 exposure

Staging default moves out of ~/.cache to <palace-root>/pi-stage (pi) and
<palace-root>/opencode-stage (opencode), resolved with mempalace's own
palace-path precedence ($MEMPALACE_PALACE_PATH -> $MEMPAL_PALACE_PATH ->
~/.mempalace/config.json -> ~/.mempalace/palace), then dirname.

Why: the convos miner keys dedup on the *staged* path, so a wiped stage plus a
sync scoped to include it prunes the drawers mined from those sources --
deleting memories, not a cache. Under ~/.cache that state was reachable by
anything treating a cache as disposable. Staging inside the palace makes the
coupling structural: the stage cannot be wiped without touching the palace
itself. Overrides ($MEMPALACE_PI_STAGE / $MEMPALACE_SESSION_STAGE, --stage) are
unchanged. Note the old default had never been created on any host, so this
closed a latent hazard, not a live one.

Measured, and the docs now claim only this much: sync prunes only within the
scope it is given -- wing-only, 1299 scanned / 1299 out of scope / 0 removed;
scoped at the palace root, 651 kept / 648 out of scope. The previous blanket
"sync prunes every drawer" wording overstated it, which is a liability: the next
reader disproves the overstatement and discards the real constraint with it.

Also in this change:
- cron log dir ~/.cache/mempalace-session -> ~/.cache/mempalace-logs. The stage
  left that namespace, so the old name now read as "the stage".
- AGENTS.md: the convos miner *does* check mtime (verified against upstream
  convo_miner.py); the previous "no mtime check" claim was wrong.
- smoke-test assertions use `mktemp -d` for --sessions-dir. One pointed at /tmp,
  which still held earlier synthetic transcripts, so a --dry-run exported a fake
  session into the real stage: --dry-run skips the mine, not the export.

docs/phase-1-exposure-runbook.md -- the newt/DNS/auth step that RFC 001 and the
synlig runbook leave open (runbook section 4, items 2 and 5). Port 8765 at /mcp,
newt targets 172.17.0.1, and the authentication is the single shared bearer
token (RFC 6.2, decided 2026-08-09) rather than per-device proxy users. The
latter cannot work today: mempalace validates exactly one token, and Pangolin's
SSO/PIN/password are browser-shaped while every client here is a headless
JSON-RPC POST -- enabling that protection breaks the clients it protects. The
per-device axis that *does* exist is the feeder's SSH key + per-device inbox.

New finding recorded there: a loopback bind does not merely 403 behind a tunnel
(already known, runbook 2.4) -- it also silently starts the server with no token
at all, because auto-minting is gated on the bind being non-loopback.

extensions/pi/README.md: the HTTP transport IS authenticated as of mempalace
3.6.0; the "sessionless and unauthenticated" note dated from the v1.3.0 era.
Closes the RFC section 8 Phase-0 hygiene item.

docs/synlig-primary-runbook.md

@@ -128,7 +128,13 @@ standing up a network-reachable service while you were asleep was not mine to de
 
 ## 4. Tomorrow, in order
 
-1. **Pangolin update on nyvaken** (yours).
+> **2026-08-12: items 1–2 and 5 now have their own runbook —**
+> [`phase-1-exposure-runbook.md`](./phase-1-exposure-runbook.md). Pangolin on nyvaken is updated (done).
+> newt is still missing on synlig. That doc also records why per-device Pangolin users are the wrong layer,
+> and an additional loopback finding: a loopback bind does not merely 403, it also silently starts the
+> server with **no token at all** (auto-minting is gated on the bind being non-loopback).
+
+1. **Pangolin update on nyvaken** (yours). ✅ done 2026-08-12.
 2. **⚠️ synlig has no tunnel client.** `docker ps` shows only the Gitea runner and digikam — no `newt`.
    Pangolin on nyvaken cannot reach synlig by itself; synlig needs a newt container (or an equivalent
    outbound tunnel) added. Easy to miss because Pangolin will look healthy on its own side. If newt runs