correct two claims about agents that the SDK disproves

docs/per-user-linux-accounts.md carried the reasoning that per-user agents were
a large piece of work, and both halves of that reasoning were wrong.

The SDK does have somewhere to put a uid — spawnClaudeCodeProcess, documented
for running Claude Code in VMs and containers — so a member's turn does not have
to become its own process. And the credential claim was backwards: the proxy
holds the OWNER'S credential, reading the owner's own ~/.claude/.credentials.json,
so pointing a member at it spends the owner's account on the member's turns.
The previous handoff had already retracted that one; the doc had not caught up,
which is how a retracted claim stays live.

Corrected in place rather than deleted, with what was believed and why it was
wrong, because the superseded version is the interesting part: the first claim
is what made agents look like a later stage than they are.

Adds the constraint that actually is out of scope, which the old text never
stated: no platform process ever runs as a member, because the sidecar holds
POSTGRES_URL and the JWT secret.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

COMMS/sidecar-app-store/2026-08-11-per-user-claude-handoff.md

@@ -38,11 +38,15 @@ them. Installed SDK is **0.2.59**; `package.json:31` pins `^0.2.41`.
 the SDK also needs to reach the spawned process in a way `setpriv` breaks, this whole approach is wrong and
 the fallback is the earlier plan (member turn as its own process).
 
-Second stale claim, already corrected once: `docs/per-user-linux-accounts.md:230` still says a member's
-`claude` "needs only `ANTHROPIC_BASE_URL` pointed at the proxy and no key of its own." The previous handoff
-§5 retracted that. **Both passages need editing; neither has been edited.** Left alone deliberately so this
-document is the record of what was believed when the code was written, rather than the doc silently agreeing
-with the code.
+Second stale claim, already retracted once by the previous handoff §5:
+`docs/per-user-linux-accounts.md:230` said a member's `claude` "needs only `ANTHROPIC_BASE_URL` pointed at the
+proxy and no key of its own." That is backwards — the proxy holds the **owner's** credential
+(`sidecar/claude/proxy.ts:7` reads the owner's own `~/.claude/.credentials.json`), so pointing a member at it
+spends the owner's account on their turns.
+
+**Both passages have now been corrected in `docs/per-user-linux-accounts.md`** (same commit range as the code).
+The superseded text is in that file's git history. If you are reading this handoff against an older checkout,
+the doc is the one that moved.
 
 ---