docs: the governing principle — every LLM request is reconstructable from the session log

The reconstructability RFC is the principle's home: model-visible ⟺
logged in both forms, the mechanism (boundary derivation + header
fold), the enforcement (write-time round-trip guard, the dev
invariant), the corollaries ranked (prefix-cache stability first), the
MiniCode lineage with the provenance arrow inverted, and the
alternatives it beat — including the stateful transmission client
whose three-design archaeology lives in PR #162.

Placements per the one-home-per-fact taxonomy: a standing-order line in
root AGENTS.md (with displacement trims to stay inside the 1,575-word
ceiling), the principle statement in architecture.md § Session Log and
its Turn Flow lines (condensed to the ratcheted 1,630 ceiling), the
request-envelope section in core-data-structures/core.md with the
LlmCallConfig paste, both review-requested FIXMEs
(FIXME(call-config-shape) beside the type, FIXME(catalog-verbs) at the
catalog's drift-gate note), cookbook rows redirected off agent/request
(tool filtering → system-prompt/assemble, plan-mode prompt → sections/
inject()), and the llm/stream JSDoc stating the frozen-request
contract. RFC index and all generated catalogs regenerated.

packages/llm/llm/src/index.ts

@@ -26,10 +26,14 @@ declare module 'cordis' {
 
   interface Events {
     /**
-     * Waterfall around every streaming model call (retry, caching, routing).
+     * Waterfall around every streaming model call (retry, replay, routing).
      * Bound to the {@link LlmService}; call `next()` to reach the resolved
      * adapter's stream, or yield your own chunks to short-circuit.
-     * @param options - the full request; listeners may rewrite it before delegating.
+     * @param options - the full request. A LOOP-built request arrives
+     *   deep-frozen (mutation throws): its content is a pure function of the
+     *   session log (the reconstructability RFC), so listeners read it, never
+     *   rewrite it. A hand-built one-shot (compaction summarize) is the
+     *   caller's own object and stays mutable here.
      * @mode waterfall
      */
     'llm/stream'(this: LlmService, options: GenerateOptions, next: () => AsyncIterable<StreamChunk>): AsyncIterable<StreamChunk>