Report a storage fault on the dependency scratch as scratch_io_failed - #533

…iagnostics, dependency-scratch storage fault code (#536)

## What

One change set that carries four reviewed pull requests together, so the release gate and the parity sweep run once on the exact tree that ships. Each of the four was reviewed and green on its own; this branch is the first, #536, plus merges of the other three. No line was rewritten.

- #533 Report a storage fault on the dependency scratch as scratch_io_failed
- #534 run_json: report the recorded failure when the internal report sink is refused
- #535 entrypoint: forward an opt-in report descriptor to run_json
- #536 run_json: report the run profile and jailed arena admission in the diagnostics

### Dependency scratch fault (from #533)

A read, write or resize fault on the scratch that holds waiting requests now ends the run as `scratch_io_failed`, a non-retryable `resource` failure, instead of `engine_invariant`, as the exit-scratch consumer already did for the same storage status. A failure the storage layer had already recorded keeps its own code. The run-failure catalog is unchanged. The change is in `require_dependency_scratch` (`src/native_execution_consumer.cpp`) and adds no net lines, so the file keeps its line count and the documentation line anchors stay valid.

### Typed failure for a refused internal report sink (from #534)

On the default route `run_json.py` installs an internal report sink. When the engine refused it, for example because the scratch arena descriptor, size or profile flag in the environment was unusable, the host reported `engine_invariant` and dropped the failure the engine had recorded. It now reads that record before the strategy state is freed and reports it (`report_sink_failed` with reason `arena_backing` for an unusable arena). If the engine recorded nothing, the previous message and code are kept. No success path changes.

### Opt-in report descriptor in the container entrypoint (from #535)

`PINEFORGE_REPORT_SINK_FD=<n>` makes the entrypoint pass `--report-sink-fd <n>` to `run_json.py`, for a caller that opened the descriptor for the report records itself. The value is forwarded unchanged, an empty value as an empty argument, and `run_json.py` stays the only validator (a number below 3, 5, a phase descriptor and a non-number are refused with its usual text and exit 2, mapped to 4 by the entrypoint). With the variable unset nothing changes.

### Run profile in the report diagnostics (from #536)

Every executed success report carries two additive `diagnostics` keys: `run_profile` (`"jailed"` or `"unjailed"`, fixed when the run starts) and `scratch_arena_jailed` (true only when the jailed profile ran and the native scratch arena admission succeeded). The flag comes from the actual admission result, never from the environment. It records the checked profile and the admission; it is not an independent check of operating-system confinement. Failure, capability and validate-only documents, and every existing key and its order, are unchanged. The replay converter keeps both keys. Python only: no native export, no C++ change.

## Tests

Each change keeps the tests it was reviewed with, committed before the fix so each fails on the unchanged tree for the stated reason: the dependency-scratch fault rows (`engine_invariant` observed), the unjailed sink refusal rows (twelve real-module rows and a free-order double), the entrypoint forwarding rows (the logged argument vector lacks the option), and the profile rows (both keys absent). The faults in the first group are injected through a backing double; no claim is made that a real disk `EFBIG` reaches that helper.

## Compatibility

- A host that matched `engine_invariant` for a dependency-scratch storage fault now sees `scratch_io_failed` (class `resource`, not retryable).
- A host that matched `engine_invariant` for a refused internal report sink on the default route now sees `report_sink_failed` / `arena_backing` for the cases above.
- Two additive keys in the success report `diagnostics` object; one opt-in environment variable. The 1.8.0 changelog describes all four.

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