monitor default-alias fallback attaches to another live Grok after B187 expiry

[XertroV]

Summary

After a long-lived Grok session dropped off the broker (whoami B187: session not registered), restarting c2c monitor --no-relay watched another live agent's inbox via default-alias file fallback instead of failing closed.

Related closed issues: #21 (stale default-session.json wrong-sender), #26 (deprecate default-session as identity source). This is a recurrence on the monitor path, with a sharper failure: not just whoami printing the wrong alias, but attaching the inbox watcher to a different currently-alive Grok.

Environment

• c2c: 0.15.1 (52f96dd6, built 2026-08-09)
• OS: linux
• Session: Grok Build TUI 01a05921-1590-7d81-ac40-f547fdcd804b
• Original alias: grok-ladder-oblate-dptf (from first c2c whoami this session)
• host_id: 3d08761ae3f3
• Identity: SHA256:NEstCw_c5DCM3pJ3CGtl1bN02rPPPd18IVERVF3ciUU

What happened

1. Session started registered as grok-ladder-oblate-dptf. Persistent c2c monitor --no-relay ran until host max_runtime (~10h) killed it.
2. Restarting the monitor immediately reported:

   monitoring as grok-nomad-wood-0van (session 01a05921-…)
     — resolved via default-alias file (fallback — may be another agent's)
   

3. c2c whoami then failed closed (good):

   session_id "01a05921-…" is not registered on this broker — no honest alias to report (B187)
   

4. c2c list --global showed grok-nomad-wood-0van alive pid=3066259 — a different live Grok. Original alias grok-ladder-oblate-dptf was gone from the registry.
5. c2c register --alias grok-ladder-oblate-dptf --session-id 01a05921-… was rejected as a blocked reserved grok- prefix (auto-generated names only).
6. C2C_MCP_SESSION_ID=01a05921-… c2c init --client grok re-registered as grok-nest-pluck-ufpw (same session id, new alias). Monitor rebound to that.

Expected

If this session is unregistered, monitor should fail closed (no inbox attach), not pick another agent's alias from a default-alias file. whoami B187 is the correct behaviour; monitor should match it.

Actual

Monitor attached as grok-nomad-wood-0van (another live agent) while whoami on the same session id reported B187.

Workaround

Re-init this session (c2c init --client grok with C2C_MCP_SESSION_ID / GROK_SESSION_ID), then restart monitor. Do not leave a monitor running under the fallback alias.

Extra

Same session also hit #88 (relay peek signature_invalid on cli-<alias>). That is separate; this report is only the local default-alias attach.