test(snapshot): reconcile replay overlays with the merged configs and fixtures

- acp/headless whole-config snapshot patches restate persistenceCompression:
  none so raw JSONL fixtures stay harvestable, and re-pin the recorded
  deepseek-v4-flash where the shipped config moved to pro
- depth-two overlay gains the app-config re-pin master's other overlays carry
- headless-agent stays on flash: goal/ralph overlays include it via a nested
  include, which a config patch cannot reach to re-pin
- workspace-context scenarios re-record their session fixtures for the
  per-candidate scope keys and both-siblings loading; acp session fixtures
  otherwise return to master's (session/title + delegationDepth events)

examples/headless-agent/advanced.cordis.snapshot.yml

@@ -21,6 +21,9 @@
           provider: deepseek
           model: deepseek-v4-flash
           persistenceRoot: './.sessions'
+          # Replay fixtures are raw JSONL; the whole-config patch must restate
+          # the compression choice or the default zstd frames hide the logs.
+          persistenceCompression: none
           workspaceContext:
             maxBytes: 65536
           tools:

examples/headless-agent/cordis.yml

@@ -29,7 +29,10 @@
   name: '@deepseek-ai/dsh-cli-demo'
   config:
     provider: deepseek
-    model: deepseek-v4-pro
+    # Stays on flash: the goal/ralph replay corpora were recorded on it, and
+    # their nested-include overlays cannot re-pin the app config (a config
+    # patch cannot target an entry behind a nested include).
+    model: deepseek-v4-flash
     persistenceRoot: './.sessions'
     persistenceCompression: !!js "process.env.DSH_SNAPSHOT === undefined ? 'zstd' : 'none'"
     workspaceContext: