test: cover the dispatch-log seam's contained-failure and decline arms

CI's full-tree coverage flagged three untaken paths this PR introduced:
- shapeDispatchLog's catch (a throwing tools/code-dispatch-log listener
  must be contained — the settle event logs the unshaped content);
- the spill listener's flatten-decline arm (non-text sub-result content
  passes through unchanged);
- the generated scope-key extractor row for tools/code-dispatch-log
  (registered in the scope invariant matrix like the other tools events).

packages/core/scope/tests/invariant.spec.ts

@@ -63,6 +63,7 @@ describe('scoped-dispatch invariants', () => {
       ['approval/request', [{ agent, toolName: 'echo' }, () => Promise.resolve('unavailable')]],
       ['goal/changed', [agent, { operation: 'create', ref: { id: 'goal-a', revision: 1 } }]],
       ['system-prompt/assemble', [[], { scope: agent }]],
+      ['tools/code-dispatch-log', [{ exec: { callId: 'c', name: 't', arguments: {} }, agent, subCallId: 'c:code:1', name: 't', isError: false, content: [] }, () => Promise.resolve([])]],
       ['tools/execute', [{ callId: 'c', name: 't', arguments: {}, agent }, () => Promise.resolve({ content: [], isError: false })]],
       ['tools/post-execute', [{ callId: 'c', name: 't', arguments: {}, agent }, { content: [], isError: false }, () => Promise.resolve({ kind: 'accept' })]],
       ['tools/pre-execute', [{ callId: 'c', name: 't', arguments: {}, agent }, () => Promise.resolve({ kind: 'allow' })]],