fix(#2406): stop Codex config.toml from double-registering agent roles (#2432)

* fix(#2406): stop Codex config.toml from double-registering agent roles

generateCodexConfigBlock emitted an [agents.<name>] role table per agent
pointing config_file back at the standalone agents/<name>.toml Codex
already auto-discovers, so every install declared each role twice in
one config layer and Codex logged a duplicate-role warning per agent.
Remove the redundant role-table loop; the standalone per-agent TOML is
now the sole canonical registration source. The existing marker-truncate
and leaked-section stripping in mergeCodexConfig already clean up legacy
[agents.gsd-*] tables from prior installs, so updates converge to zero
duplicates without any new migration path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(#2406): regenerate fixtures + lint gate-prep

* fix(#2406): repair failing tests after gate verification

* docs(#2406): add changeset for Codex duplicate agent-role fix

Adds the missing .changeset/*.md fragment for the Codex config.toml
double-registration fix, closing the PR-gate finding from review.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(#2406): backfill changeset pr (#2432)

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

.changeset/2406-codex-agent-role-double-registration.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 2432
+---
+**Codex installer no longer double-registers each agent role in `config.toml`, eliminating one duplicate-role startup warning per agent** — `generateCodexConfigBlock` stopped emitting `[agents.gsd-*]` tables whose `config_file` pointed back at the same standalone TOMLs Codex already auto-discovers under `$CODEX_HOME/agents/`; reinstalling over an existing config also drops any legacy managed role tables left by a prior install while preserving unrelated user config and the user's own AgentsToml scalars. (#2406)