Merge origin/master into feat/tui-package

Master unifies every live agent with its exact SessionId and moves declarative startup failures to agent-loop/config-start-failed. Keeping the branch’s AgentId label binding would let the TUI target the wrong lifecycle after reload and would miss asynchronous resume failures.

Resolve that contract migration by giving the selected terminal front door the same generated or resumed SessionId as agent-core, mounting the front door first, and entering fullscreen only after the matching root appears. Refresh the source-derived catalogs and keyless terminal goldens so Code Mode, workflow, Cordis-tool, and transient UI scenarios all exercise the merged identity model.

docs/rfc/INDEX.md

@@ -20,7 +20,6 @@ Generated by `pnpm run gen-rfc-index` from the RFC tree — never edit by hand;
 
 | Title | First proposed |
 |---|---|
-| [Unify the agent id and the session id](proposed/simplification/2026-06-20-unify-agent-and-session-id.md) | 2026-06-20 |
 | [Prune dead public and result surface](proposed/simplification/2026-07-04-prune-dead-core-spine-surface.md) | 2026-07-04 |
 
 ### Architecture
@@ -99,6 +98,7 @@ Generated by `pnpm run gen-rfc-index` from the RFC tree — never edit by hand;
 | [Prune dead methods from the persistence seam](implemented/simplification/2026-06-20-prune-dead-seam-methods.md) | 2026-06-20 |
 | [Keep one public stop primitive](implemented/simplification/2026-06-20-public-agent-stop-surface.md) | 2026-06-20 |
 | [Stop mirroring durable boundaries as agent events](implemented/simplification/2026-06-20-remove-agent-boundary-mirror-events.md) | 2026-06-20 |
+| [Unify the agent id and the session id](implemented/simplification/2026-06-20-unify-agent-and-session-id.md) | 2026-06-20 |
 | [Split the filesystem seam — provider text mutations plus the `dsh-fs-policy` plugin](implemented/simplification/2026-06-26-fsspec-style-fs-seam.md) | 2026-06-26 |
 | [Stop mirroring the token stream as an agent event](implemented/simplification/2026-07-02-remove-stream-chunk-mirror.md) | 2026-07-02 |
 | [Drop the `image` content block until a path can honor it](implemented/simplification/2026-07-04-drop-image-content-block.md) | 2026-07-04 |