Parent: #548
A strict two-file reduction shows that an imported class method loses contextual callback parameter types when an unrelated class member makes the complete class schema unsupported. TypeScript 6.0.3 and the native TypeScript preview report zero diagnostics; ReleaseFast Home reports TS7006 for both the direct and nested callback parameters.
The production symptom is the repeated doc.indented callback family in the pinned Zod 4.5.2 corpus. The general defect is all-or-nothing imported-class transfer: the fallback preserves member names but degrades method types to any even when the individual method contract is transferable.
Acceptance criteria:
- preserve transferable imported class method signatures when sibling members are unsupported
- retain recursive self types so nested method callbacks remain contextually typed
- do not broadly admit unsupported class graphs or add corpus diagnostics
- add positive and negative multi-file regressions
- match TypeScript 6.0.3 and the native preview on a fair standalone oracle
- require full checker and Program suites, ReleaseFast, and an exact unchanged-corpus diagnostic diff
- publish the result in the performance record and README