Merge worktree-hooks-b-bash-seam into worktree-hooks-c-interception

Bring the interception-seams branch onto current master (via A→B). The
substantive reconciliation is master's compaction `agent/pre-step` serial seam
meeting C's interception seams:

- types.ts: keep BOTH master's `agent/pre-step` AND C's new interception events
  (`agent/prompt-submit`, `agent/session-start`, `agent/turn-continuation`→
  `ContinuationDecision`); drop the turn-mirror declarations (removed on A).
- loop.ts: the merged per-turn order is `turn/start` → per queued msg
  `agent/prompt-submit` (rewrite/inject/block) → (fully-blocked ⇒ zero-step
  `rejected`) → per step: drain steering → assemble system prompt →
  `agent/pre-step` (compaction, OUTSIDE the step) → `step/start` → single
  `deriveMessages()` → model → tools/pre-execute·dispatch·post-execute. No
  turn-mirror emits; `closeTurn()` is the A-simplified single-call form.
- Docs (architecture, core.md, agent/agent-loop READMEs, catalog) reconciled to
  show C's interception seams alongside `agent/pre-step`, no turn/step mirrors.
- rfc/README: dropped the stale `proposed/` compaction row (master moved that RFC
  to implemented/); kept C's new `pre-tool-input-rewrite` proposed row.
- interception.spec.ts: migrated its two `agent/turn-end` reason collectors to
  the `turn/end` session event, and ADDED a cross-test proving a
  `prompt-submit` rewrite + additionalContext is VISIBLE to an `agent/pre-step`
  listener on the same turn — pinning the merged seam ordering (compaction sees
  the post-prompt-submit surface, not stale history).

docs/rfc/README.md

@@ -44,7 +44,6 @@ Do NOT write one for a mechanical or local choice (a variable name, a one-file r
 | [Agent Client Protocol (ACP) support for external editors](proposed/feature/2026-06-14-acp-agent-client-protocol.md) | 2026-06-14 |
 | [Multiplex concurrent ACP sessions over one connection](proposed/feature/2026-06-14-acp-multi-session.md) | 2026-06-14 |
 | [Optional Code Mode — model writes TypeScript against an SDK of all tools](proposed/feature/2026-06-15-optional-code-mode.md) | 2026-06-15 |
-| [Compaction as a capability seam (abstract contract + basic backend)](proposed/feature/2026-06-18-compaction-capability-seam.md) | 2026-06-18 |
 | [Pre-tool input rewrite — a consistent design](proposed/feature/2026-06-30-pre-tool-input-rewrite.md) | 2026-06-30 |
 
 ### Simplification
@@ -52,7 +51,6 @@ Do NOT write one for a mechanical or local choice (a variable name, a one-file r
 | 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 |
-| [Stop mirroring durable boundaries as agent events](proposed/simplification/2026-06-20-remove-agent-boundary-mirror-events.md) | 2026-06-20 |
 
 ### Architecture
 
@@ -84,6 +82,7 @@ Do NOT write one for a mechanical or local choice (a variable name, a one-file r
 | Title | First proposed |
 |---|---|
 | [Rich ACP bash rendering — the terminal card (`_meta`) and command classification](implemented/feature/2026-06-18-acp-terminal-and-tool-rendering.md) | 2026-06-18 |
+| [Compaction as a capability seam (abstract contract + basic backend)](implemented/feature/2026-06-18-compaction-capability-seam.md) | 2026-06-18 |
 | [Subagent capability seam](implemented/feature/2026-06-21-subagent-capability-seam.md) | 2026-06-21 |
 | [ACP subagent backend (out-of-process delegation)](implemented/feature/2026-06-22-acp-subagent-backend.md) | 2026-06-22 |
 | [The `todo_write` tool — model task list as event-sourced session state](implemented/feature/2026-06-29-todo-write-tool.md) | 2026-06-29 |
@@ -99,6 +98,7 @@ Do NOT write one for a mechanical or local choice (a variable name, a one-file r
 | [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 |
 | [Fold trace-only session facts into load-bearing events](implemented/simplification/2026-06-20-collapse-trace-only-session-events.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 |
 
 ### Architecture
 
@@ -123,7 +123,7 @@ Do NOT write one for a mechanical or local choice (a variable name, a one-file r
 | [Branded IDs everywhere they belong](implemented/architecture/2026-06-20-branded-ids.md) | 2026-06-20 |
 | [Extract example apps into packages](implemented/architecture/2026-06-20-extract-example-app-packages.md) | 2026-06-20 |
 | [Event-domain semantics — session is the fact log, agent is the live surface](implemented/architecture/2026-06-30-event-domain-semantics.md) | 2026-06-30 |
-| [stdin + extra env on the bash seam — a trusted-plugin surface](implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md) | 2026-06-30 |
+| [stdin + extra env on the bash seam](implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md) | 2026-06-30 |
 
 ### Process