docs: add RFC 001 — global palace with local fallback (mempalace-edge)

Design for moving from one MemPalace per machine per harness to a single
primary palace with per-machine offline fallback, plus the source-verified
archaeology behind it.

Key decisions recorded:

- Sync operations (MCP tool calls), not databases. Embeddings are computed
  client-side and are not portable across architectures; the KG `triples`
  table has no UNIQUE(subject,predicate,object,valid_from) and its ids embed
  datetime.now(), so row copies duplicate facts. Replaying tool calls is
  idempotent where it matters.
- Implement as `mempalace-edge`, a local stdio MCP proxy (child mempalace-mcp
  + HTTPS to the primary + outbox.sqlite), not as per-harness patches. Needs
  zero mempalace internals, so it serves pi, opencode and the CLI alike and
  survives mempalace upgrades.
- Merged reads (query both, re-sort, dedupe by drawer id) give fleet-wide
  recall without replication — which is why Phase 3 (pull replication) is
  deferred: "own writes plus whatever it can reach" is good enough.
- Per-wing replication policy: curated/content-addressed wings replicate,
  mined code/docs stay local (derived, re-mineable, path-dependent ids).

Also documents two silently destructive footguns to avoid during rollout:
`--palace` vs MEMPALACE_PALACE_PATH (the KG follows the flag only, so
`mempalace serve` can start with a silently empty knowledge graph), and
`mempalace sync`, which is gitignore-aware drawer deletion rather than
replication and would wipe fleet memory when run from a host lacking the
repos. Notes that mempalace 3.6.0's `serve` already ships token auth + TLS,
making the "unauthenticated, front it with a proxy" notes elsewhere stale.

Includes an evidence index mapping each claim to file:line in mempalace
3.6.0, and four upstream candidates (origin_host provenance, per-wing ACL,
mempalace_kg_supersede missing from service.py WRITE_TOOLS, and a
sync --refuse-shared guard).

AGENTS.md

@@ -13,6 +13,8 @@ install.sh              # Idempotent installer — see "What install.sh does" be
 ARCHITECTURE.md         # Canonical spec: diagrams, setup recipe, ops notes, upstream roadmap
 README.md               # Human-facing quickstart + per-tool usage reference
 SKILL.md                # Agent skill (symlinked into ~/.agents/skills/ on install)
+docs/
+  rfc-001-global-palace.md  # Design: one primary palace + per-machine local fallback (mempalace-edge)
 bin/
   mempalace-docs        # Docs-only MemPalace miner (bash wrapper)
   mempalace-session     # Opencode session → MemPalace bridge (bash + inline Python)