Mutation→context merge primitive across the stack

The @client(merge=[context, ...]) decorator lets a mutation patch its
return value directly into the cached context bundle by matching the
mutation's Output type against each context-function's Output type
to identify the slot, then splicing server-side. Kernel runs
splice_slot on the response to apply locally — no refetch, no
invalidate-cascade.

Lands H14, H15, H16, M19, M20 from ISSUES.md.

Backends (Django + FastAPI):
  _resolve_merges() in both executors walks @client(merge=...) targets,
  resolves the per-context slot via types_match_for_merge, and emits
  {context, slot, value, params?} entries on the response. Param
  auto-scoping mirrors _resolve_invalidation's tier-1 logic.

Frontend kernel (mizan-base):
  Response handler reads the merge[] array and applies splice_slot
  for each entry — locates the cached context bundle by name+params,
  overwrites the named slot with the new value, notifies subscribers.

Core (mizan-python):
  @client decorator extended with merge= parameter. Schema export
  threads merge metadata onto the OpenAPI x-mizan-functions entries.

Examples / fixtures:
  fastapi-react-site harness exercises merge + Playwright spec covers
  the end-to-end happy path (mutation → instant UI update without
  network refetch). AFI fixture's rename_user function is the
  canonical merge target.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ISSUES.md

@@ -18,8 +18,13 @@ Identified by domain expert review (Cloudflare, Serverless, Vercel, React Query,
 - ~~H10~~ _meta always fresh dict
 - ~~H11~~ Python normalizes True→"true" for cross-language HMAC
 - ~~H13~~ isValid checks all required fields are touched
+- ~~H14~~ `@client(merge=...)` primitive — kernel splices return value into cached context, no refetch
+- ~~H15~~ Schema export handles `BaseModel | None` return types
+- ~~H16~~ Generated `react.tsx` imports per-function `*Output` types
 - ~~M11~~ execute_function return type includes HttpResponseBase
 - ~~M18~~ registerContext cleanup uses ?. (no crash)
+- ~~M19~~ `list[BaseModel]` returns reach the wire as bare arrays (RootModel-based rename, no `{result: ...}` wrap)
+- ~~M20~~ `initSession()` gated on `configure({session: bool})` (Django default-on, FastAPI opt-out)
 
 ## Remaining Critical