fix(workspace-context): restore the no-unrepresented-commit gate after master merge

The master merge rewrote reconcileInstructionContext and dropped this
branch's gate: when no transition survives rendering (tiny budgets
produce notice-only text), emit nothing and commit nothing so the next
pass retries. Restore it, align the inbox one-byte test with that
contract (an unrepresentable change is held back, not committed at 1
byte), and move the nested-retry test's probe assertions to sync time
where reconciliation now runs. Also restore master's markdown spec
casts lost in an earlier merge.

packages/client/ui-primitives/tests/markdown.spec.tsx

@@ -162,7 +162,7 @@ describe('MarkdownText', () => {
     expect(() => tokenizer?.call({
       parser: { constructs: { attentionMarkers: {} } },
       previous: null,
-    }, {}, () => undefined, () => undefined)).toThrow(
+    } as never, {} as never, () => undefined, () => undefined)).toThrow(
       'micromark CommonMark attention markers are unavailable',
     )
   })