docs: MEMPALACE_PI_DEVICE now also attributes drawers

Follow-up to c64ffa1, which changed the --agent default but left --help
claiming $USER. Fixes that text and states in README/ARCHITECTURE that the
device label reaches the palace as added_by, since mempalace stores neither the
machine nor the harness on a write.

ARCHITECTURE.md

@@ -196,6 +196,14 @@ server to mine its own local copy of that inbox over the same HTTP
 `$MEMPALACE_PI_SSH_TARGET`; see `--help` for the rest
 (`MEMPALACE_PI_SSH_CONFIG`, `MEMPALACE_PI_REMOTE_PATH`, `MEMPALACE_PI_DEVICE`).
 
+**Attribution.** `MEMPALACE_PI_DEVICE` is not only the inbox directory name: it
+also defaults `--agent` to `pi@<device>`, which reaches the palace as each
+drawer's `added_by`. This matters because mempalace records neither the
+originating machine nor the harness on a write, and a shared bearer token leaves
+the server unable to tell clients apart. Without it, attribution has to be
+reconstructed after the fact from the inbox path and the `pi_*.jsonl` filename —
+which works for mined transcripts but not for anything filed by hand.
+
 **Filters:** two gates, both required — stricter than `mempalace-session`'s
 single filter because pi's transcripts have a failure mode opencode's don't:
 

README.md

@@ -573,8 +573,10 @@ exports. `--mode remote` (or `--mode auto`, which detects
 the palace host and asks the server to mine its own local copy. Requires
 `$MEMPALACE_PI_SSH_TARGET` (`user@host:path`); see `MEMPALACE_PI_SSH_CONFIG`,
 `MEMPALACE_PI_REMOTE_PATH`, and `MEMPALACE_PI_DEVICE` in `--help` for the
-rest. Deploying that primary — newt, DNS, and why the auth is a shared bearer
-token rather than per-device proxy users — is
+rest. `MEMPALACE_PI_DEVICE` also defaults `--agent` to `pi@<device>` so each
+drawer's `added_by` records which harness and which machine produced it —
+mempalace itself stores neither. Deploying that primary — newt, DNS, and why the
+auth is a shared bearer token rather than per-device proxy users — is
 [`docs/phase-1-exposure-runbook.md`](docs/phase-1-exposure-runbook.md).
 
 ---

bin/mempalace-pi-session

@@ -212,7 +212,11 @@ Options:
                          assistant text, tool results excluded (default: 1000).
                          Catches abandoned sessions whose bulk is injected
                          skill/context text in the user prompt.
-  --agent <name>         Agent name recorded on drawers (default: $USER)
+  --agent <name>         Agent name recorded on drawers. Defaults to
+                         pi@$MEMPALACE_PI_DEVICE when that is set, else $USER.
+                         The palace records neither the harness nor the machine
+                         on a write, so this one string is what makes a drawer
+                         attributable to both.
   --sessions-dir <path>  Path to pi sessions dir (default: $PI_SESSIONS_DIR
                          or ~/.pi/agent/sessions)
   --stage <path>         Staging root (default: $MEMPALACE_PI_STAGE, else