test(issue-13): give each purge test fresh conversation ids

Round-2 review of 7610258 (planner-reviewer-claude-01, reviewer-grok-01,
N2): the purge tests used two fixed UUIDs, while conversation_in_use scans
every process on the host. A review job's delegation wrapper carries the
whole brief - including this file's diff and so both constants - on its
command line, so five tests read "in use" for as long as that wrapper
lived. Reproduced here: this job's own wrapper named both constants and
the same five tests failed.

- tests: `conv` / `other` fixtures hand every test a fresh uuid4 and
  assert that no live process names it yet; the helpers already took the
  id as an argument. With a bystander process naming the old constants,
  the file passes 21/21 and the brief's required set 248/248
- orc-onboard SKILL.md: any live process whose command line contains the
  UUID blocks the purge, not only a resumed session (review R-2), and how
  to find it

No product code changes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HCGpJXhSZasJLU38ksDghe

.agents/skills/multi-agent-mux-orc-onboard/SKILL.md

@@ -26,7 +26,7 @@ Registers an orchestrator session UUID into the `orchestrator_uuids` list of `.m
 ### Options
 - `--uuid <uuid>`: Explicitly register the specified orchestrator session UUID.
 - `--remove <uuid>`: Remove the specified UUID from the `orchestrator_uuids` list.
-- `--purge-conversation`: With `--remove`, also delete the conversation's on-disk artifacts through its agent adapter (Issue #13). Irreversible — requires `--yes`; refused (exit `5`, registration untouched) while a live process still references the conversation — including the session the command itself runs in: its session-id variable (`CLAUDE_CODE_SESSION_ID`, `ANTIGRAVITY_CONVERSATION_ID`, `HERMES_SESSION_ID`, `GROK_SESSION_ID`, `OPENCODE_SESSION_ID`) equals the UUID, or the nearest agent CLI ancestor names it on its command line. An orchestrator therefore cannot purge its own conversation from inside that very session.
+- `--purge-conversation`: With `--remove`, also delete the conversation's on-disk artifacts through its agent adapter (Issue #13). Irreversible — requires `--yes`; refused (exit `5`, registration untouched) while a live process still references the conversation — including the session the command itself runs in: its session-id variable (`CLAUDE_CODE_SESSION_ID`, `ANTIGRAVITY_CONVERSATION_ID`, `HERMES_SESSION_ID`, `GROK_SESSION_ID`, `OPENCODE_SESSION_ID`) equals the UUID, or the nearest agent CLI ancestor names it on its command line. An orchestrator therefore cannot purge its own conversation from inside that very session. Any live process whose command line contains the UUID counts, not only a resumed session — an editor, a `grep` or a delegation wrapper whose prompt merely mentions it blocks the purge too; if it is refused, find the process with `ps -axww | grep <uuid>`.
 - `--yes`: Skip the `--purge-conversation` confirmation (without it the script prints the danger notice and exits `4`).
 - `--agent <name>`: Adapter to purge with (`claude|agy|hermes|grok|opencode|codex`). Default `auto`: each adapter is asked whether it owns an artifact for the UUID (`agy` → `~/.gemini/antigravity-cli/conversations/<uuid>.db` etc.). Needed because `orchestrator_uuids` stores bare UUIDs, not the agent kind.
 - `--list`: Display all currently registered orchestrator UUIDs.