Rename grace (formerNames) for peers' pins

What it does

After a session is renamed, peers that pinned the old name are still delivered to for a grace period, through a formerNames field on the session's record.

Source

ganja-code-uul (a rename grace, formerNames).

The bead is closed when this issue is published, with its external reference pointing here (#38).

File and line references in this issue are to main as of 75a7a92.

Against the three criteria

• Direction (README): The README says nothing about addressing between sessions; the nearest direction it states is ganja as the control plane (README.md:16-18).
• Today's terminal users: After a rename, a peer's old pin becomes an honest refusal (NameMoved or Unknown), never a silent misdelivery, and D535's list_sessions lets the peer look the new name up in one tool call.
• Evidence: formerNames is omitted on purpose (crates/ganja-tool/src/registry.rs:100). It was considered and refused twice for lack of evidence in the reference; the captain's verdict does not wait for that evidence.

Depends on

Nothing.

Verdict

• Verdict: do
• Size: S — one commit, no plan.
• Exception to the probe rule: no.
• Date: 2026-09-19
• Verdict ticket: #41

Theme: #54

Read crates/ganja-tool/src/registry.rs around line 100 and the README guidance at lines 16-18; trace how session renames and peer pins are represented. Reconcile the issue's stated grace-period behavior with its requirement that old pins refuse honestly, then make the smallest registry change and verify the renamed-session lookup behavior described here.