loop: every request is built from the log — boundary snapshot, header events, config-only waterfall

The loop is now transmission-stateless; a request is a pure function of
(session log, this step's rendered assembly, current AgentOptions):

- The reconstruction boundary is step/start: the messages snapshot is
  taken in the same synchronous frame immediately before the step/start
  append, so the request's messages are exactly the derivation over
  events[0..stepStartSeq) — an inject() from an agent/request listener
  (or any concurrent task) lands after the boundary and joins the NEXT
  request. This changes behavior for a synchronous step/start
  session/event listener that appends content (master derived after the
  append, so such a listener could reach the current request):
  agent/pre-step is the sanctioned seam for current-request content.
- agent/request is re-typed to config-only: (agent, turn, step,
  config: LlmCallConfig, next) → LlmCallConfig. The frozen seed comes
  from AgentOptions on a loop instance's first request (explicit options
  beat the logged baseline — fork overrides and resume reconfiguration
  stay correct) and from the log's folded header afterwards; listeners
  return a replacement to switch. Content shaping through the request is
  no longer expressible — model-visible content flows through the log
  channels.
- recordRequestHeader appends whatever header event the request owes the
  log before dispatch: an 'initial'/'resume' snapshot anchoring each
  loop instance, a round-trip-verified delta on change, a 'fallback'
  snapshot when the encoding cannot express it. Session.requestHeader()
  is the log's incrementally-folded baseline.
- Requests are deep-frozen before dispatch (deepFreeze exempts the
  AbortSignal — freezing one breaks AbortController.abort() outright);
  frozen + sessionId is the loop-built marker the dev invariant keys on.

Ported from #162 and re-anchored on the log: the append-extension /
frozen-end-to-end / compaction-resend / prompt-change property tests,
plus new specs for the boundary semantics, resume anchoring, and the
end-to-end theorem (every recorded request rebuilds byte-equal from the
log alone). Live cache-hit e2e (request-cache.e2e.ts) verified against
the real DeepSeek API. Snapshot goldens intentionally stale until the
single re-record after the compact/summary envelope lands.

docs/cordis-catalog/events.md

@@ -47,7 +47,7 @@ A step or turn errored. The loop reports a failure here (plus the logger) even w
 
 Types: [Agent](../core-data-structures/core.md)
 
-Source: [`packages/core/agent/src/types.ts:394`](../../packages/core/agent/src/types.ts)
+Source: [`packages/core/agent/src/types.ts:404`](../../packages/core/agent/src/types.ts)
 
 ### `agent/pre-step` — serial
 
@@ -89,15 +89,15 @@ Source: [`packages/core/agent/src/types.ts:273`](../../packages/core/agent/src/t
 
 ### `agent/request` — waterfall
 
-Waterfall: mutate the fully-assembled GenerateOptions before the model call (hooks, model switching, tool filtering, …). Call `next()` to delegate, or return without it to short-circuit. For surface mutation that must precede history derivation (compaction), use agent/pre-step instead — by the time this fires, `options.messages` is already derived.
+Waterfall: shape the step's call configuration — model switching, sampling overrides — by returning a replacement LlmCallConfig (the frozen seed is the config the loop would otherwise use). Config is ALL a listener shapes here: every request is a pure function of the session log (the reconstructability RFC), so model-visible content flows through the log channels — `inject()`, steering, prompt-submit `additionalContext`, prompt sections via `system-prompt/assemble` — never through request mutation, and the loop records whatever config the request actually uses as a `request/header*` event before dispatch. The step's messages are already snapshotted when this fires (the `step/start` boundary): an `inject()` from a listener here lands in the log but joins the NEXT request. For surface mutation that must precede the snapshot (compaction), use agent/pre-step. Call `next()` to delegate, or return an LlmCallConfig without it to short-circuit.
 
 ```ts cordis-catalog
-'agent/request'(agent: Agent, turn: number, step: number, options: GenerateOptions, next: () => Promise<GenerateOptions>): Promise<GenerateOptions>
+'agent/request'(agent: Agent, turn: number, step: number, config: LlmCallConfig, next: () => Promise<LlmCallConfig>): Promise<LlmCallConfig>
 ```
 
-Types: [Agent](../core-data-structures/core.md) · [GenerateOptions](../core-data-structures/core.md)
+Types: [Agent](../core-data-structures/core.md) · [LlmCallConfig](../core-data-structures/core.md)
 
-Source: [`packages/core/agent/src/types.ts:359`](../../packages/core/agent/src/types.ts)
+Source: [`packages/core/agent/src/types.ts:369`](../../packages/core/agent/src/types.ts)
 
 ### `agent/session-start` — emit
 
@@ -133,7 +133,7 @@ Waterfall: post-process the assembled assistant Message before tool dispatch (va
 
 Types: [Agent](../core-data-structures/core.md) · [Message](../core-data-structures/core.md)
 
-Source: [`packages/core/agent/src/types.ts:369`](../../packages/core/agent/src/types.ts)
+Source: [`packages/core/agent/src/types.ts:379`](../../packages/core/agent/src/types.ts)
 
 ### `agent/turn-continuation` — waterfall
 
@@ -145,7 +145,7 @@ Waterfall: override the turn-continuation decision via a typed ContinuationDecis
 
 Types: [Agent](../core-data-structures/core.md)
 
-Source: [`packages/core/agent/src/types.ts:382`](../../packages/core/agent/src/types.ts)
+Source: [`packages/core/agent/src/types.ts:392`](../../packages/core/agent/src/types.ts)
 
 ## `fs/*`
 
@@ -209,7 +209,7 @@ A session was created in the store.
 'session/created'(session: Session): void
 ```
 
-Source: [`packages/core/session/src/index.ts:38`](../../packages/core/session/src/index.ts)
+Source: [`packages/core/session/src/index.ts:39`](../../packages/core/session/src/index.ts)
 
 ### `session/event` — emit
 
@@ -221,7 +221,7 @@ An event was appended to a session log (sync, fire-and-forget). This is the per-
 
 Types: [SessionEvent](../core-data-structures/core.md)
 
-Source: [`packages/core/session/src/index.ts:46`](../../packages/core/session/src/index.ts)
+Source: [`packages/core/session/src/index.ts:47`](../../packages/core/session/src/index.ts)
 
 ### `session/flush` — parallel
 
@@ -231,7 +231,7 @@ Awaited durability checkpoint. The agent loop awaits `ctx.parallel('session/flus
 'session/flush'(session: Session): Promise<void> | void
 ```
 
-Source: [`packages/core/session/src/index.ts:56`](../../packages/core/session/src/index.ts)
+Source: [`packages/core/session/src/index.ts:57`](../../packages/core/session/src/index.ts)
 
 ## `subagent/*`
 

docs/cordis-catalog/services.md

@@ -163,7 +163,7 @@ get(id: SessionId): Session | undefined
 list(): Session[]
 ```
 
-Source: [`packages/core/session/src/index.ts:345`](../../packages/core/session/src/index.ts)
+Source: [`packages/core/session/src/index.ts:367`](../../packages/core/session/src/index.ts)
 
 ## `ctx.subagents` — `SubagentService`
 

docs/event-producer-consumer.md

@@ -9,22 +9,22 @@ This matrix shows which packages dispatch each harness-owned event and which pac
 | --- | --- | --- | --- | --- |
 | `agent/created` | `emit` | [`packages/core/agent/src/types.ts:248`](../packages/core/agent/src/types.ts) | [`agent`](../packages/core/agent) (`emit`) | [`stdio-agent`](../packages/ui/stdio-agent) |
 | `agent/disposed` | `emit` | [`packages/core/agent/src/types.ts:255`](../packages/core/agent/src/types.ts) | [`agent`](../packages/core/agent) (`emit`) | [`stdio-agent`](../packages/ui/stdio-agent) |
-| `agent/error` | `emit` | [`packages/core/agent/src/types.ts:394`](../packages/core/agent/src/types.ts) | [`agent-loop`](../packages/core/agent-loop) (`emit`) | - |
+| `agent/error` | `emit` | [`packages/core/agent/src/types.ts:404`](../packages/core/agent/src/types.ts) | [`agent-loop`](../packages/core/agent-loop) (`emit`) | - |
 | `agent/pre-step` | `serial` | [`packages/core/agent/src/types.ts:333`](../packages/core/agent/src/types.ts) | [`agent-loop`](../packages/core/agent-loop) (`serial`) | [`compact-basic`](../packages/compact/compact-basic) |
 | `agent/prompt-submit` | `waterfall` | [`packages/core/agent/src/types.ts:346`](../packages/core/agent/src/types.ts) | [`agent-loop`](../packages/core/agent-loop) (`waterfall`) | [`hooks-claude`](../packages/hooks/hooks-claude), [`hooks-codex`](../packages/hooks/hooks-codex) |
 | `agent/queued` | `emit` | [`packages/core/agent/src/types.ts:273`](../packages/core/agent/src/types.ts) | [`agent-loop`](../packages/core/agent-loop) (`emit`) | - |
-| `agent/request` | `waterfall` | [`packages/core/agent/src/types.ts:359`](../packages/core/agent/src/types.ts) | [`agent-loop`](../packages/core/agent-loop) (`waterfall`) | - |
+| `agent/request` | `waterfall` | [`packages/core/agent/src/types.ts:369`](../packages/core/agent/src/types.ts) | [`agent-loop`](../packages/core/agent-loop) (`waterfall`) | - |
 | `agent/session-start` | `emit` | [`packages/core/agent/src/types.ts:288`](../packages/core/agent/src/types.ts) | [`agent-loop`](../packages/core/agent-loop) (`emit`) | [`hooks-claude`](../packages/hooks/hooks-claude), [`hooks-codex`](../packages/hooks/hooks-codex) |
 | `agent/status` | `emit` | [`packages/core/agent/src/types.ts:264`](../packages/core/agent/src/types.ts) | [`agent-loop`](../packages/core/agent-loop) (`emit`) | [`acp`](../packages/ui/acp), [`invariants`](../packages/support/invariants), [`stdio-agent`](../packages/ui/stdio-agent) |
-| `agent/step-result` | `waterfall` | [`packages/core/agent/src/types.ts:369`](../packages/core/agent/src/types.ts) | [`agent-loop`](../packages/core/agent-loop) (`waterfall`) | - |
-| `agent/turn-continuation` | `waterfall` | [`packages/core/agent/src/types.ts:382`](../packages/core/agent/src/types.ts) | [`agent-loop`](../packages/core/agent-loop) (`waterfall`) | [`hooks-claude`](../packages/hooks/hooks-claude), [`hooks-codex`](../packages/hooks/hooks-codex) |
+| `agent/step-result` | `waterfall` | [`packages/core/agent/src/types.ts:379`](../packages/core/agent/src/types.ts) | [`agent-loop`](../packages/core/agent-loop) (`waterfall`) | - |
+| `agent/turn-continuation` | `waterfall` | [`packages/core/agent/src/types.ts:392`](../packages/core/agent/src/types.ts) | [`agent-loop`](../packages/core/agent-loop) (`waterfall`) | [`hooks-claude`](../packages/hooks/hooks-claude), [`hooks-codex`](../packages/hooks/hooks-codex) |
 | `fs/edit-intent` | `waterfall` | [`packages/fs/fs/src/index.ts:123`](../packages/fs/fs/src/index.ts) | [`tool-fs`](../packages/fs/tool-fs) (`waterfall`) | [`fs-policy`](../packages/fs/fs-policy) |
 | `fs/observed` | `emit` | [`packages/fs/fs/src/index.ts:138`](../packages/fs/fs/src/index.ts) | [`tool-fs`](../packages/fs/tool-fs) (`emit`) | [`fs-policy`](../packages/fs/fs-policy) |
 | `fs/write-intent` | `waterfall` | [`packages/fs/fs/src/index.ts:109`](../packages/fs/fs/src/index.ts) | [`tool-fs`](../packages/fs/tool-fs) (`waterfall`) | [`fs-policy`](../packages/fs/fs-policy) |
 | `llm/stream` | `waterfall` | [`packages/llm/llm/src/index.ts:35`](../packages/llm/llm/src/index.ts) | [`llm`](../packages/llm/llm) (`waterfall`) | [`llm-replay`](../packages/support/llm-replay) |
-| `session/created` | `emit` | [`packages/core/session/src/index.ts:38`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`emit`) | [`invariants`](../packages/support/invariants), [`session-persistence`](../packages/session-persistence/session-persistence) |
-| `session/event` | `emit` | [`packages/core/session/src/index.ts:46`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`emit`) | [`acp`](../packages/ui/acp), [`invariants`](../packages/support/invariants), [`session-persistence`](../packages/session-persistence/session-persistence), [`stdio-agent`](../packages/ui/stdio-agent) |
-| `session/flush` | `parallel` | [`packages/core/session/src/index.ts:56`](../packages/core/session/src/index.ts) | [`agent-loop`](../packages/core/agent-loop) (`parallel`) | [`session-persistence`](../packages/session-persistence/session-persistence) |
+| `session/created` | `emit` | [`packages/core/session/src/index.ts:39`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`emit`) | [`invariants`](../packages/support/invariants), [`session-persistence`](../packages/session-persistence/session-persistence) |
+| `session/event` | `emit` | [`packages/core/session/src/index.ts:47`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`emit`) | [`acp`](../packages/ui/acp), [`invariants`](../packages/support/invariants), [`session-persistence`](../packages/session-persistence/session-persistence), [`stdio-agent`](../packages/ui/stdio-agent) |
+| `session/flush` | `parallel` | [`packages/core/session/src/index.ts:57`](../packages/core/session/src/index.ts) | [`agent-loop`](../packages/core/agent-loop) (`parallel`) | [`session-persistence`](../packages/session-persistence/session-persistence) |
 | `subagent/end` | `emit` | [`packages/subagent/subagent/src/index.ts:98`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`hooks-claude`](../packages/hooks/hooks-claude) |
 | `subagent/provider-added` | `emit` | [`packages/subagent/subagent/src/index.ts:72`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`emit`) | [`tool-subagent`](../packages/subagent/tool-subagent) |
 | `subagent/provider-removed` | `emit` | [`packages/subagent/subagent/src/index.ts:83`](../packages/subagent/subagent/src/index.ts) | - | [`tool-subagent`](../packages/subagent/tool-subagent) |