fix: capture killed/aborted on record; remove internal export leakage

[slgoodrich]

Summary

Bundles four open issues into one PR (#72 and #81 deferred as features).

• synth result.killed is derived from signal but should be captured #129 — capture killed separately from signal
• tinyexec adapter: aborted/killed not captured on record path #126 — tinyexec record path: snapshot aborted/killed from ExecProcess pre-await
• v0.7: avoid inputFile double-read by threading resolved Call.stdin into realCall #102 — skip the inputFile double-read by threading Call.stdin through realCall
• _captureResultForTesting leaks into public package entries #128 — move captureResult into non-exported modules so _captureResultForTesting no longer leaks into the published .d.ts

Why

#129: replay synth conflated killed with signal !== null

execa's killed is true only when subprocess.kill() was called. A process terminated by an external signal has signal !== null but killed === false on the real result. Replay synth derived killed: signal !== null, so cassettes recorded for externally-signaled processes replayed with the wrong killed value. Both adapters now store r.killed === true on capture; serialize emits killed when defined; synth uses rec.result.killed ?? signal !== null so cassettes recorded before this change still replay correctly.

#126: tinyexec recorded aborted: false / killed: false on every call

tinyexec's Result = PromiseLike<Output> & OutputApi. Awaiting it drops the OutputApi getters (aborted, killed) that live on the ExecProcess. The adapter previously read those on the awaited Output and got undefined, so every cassette stored aborted: false/killed: false regardless of the call's outcome. The adapter's realCall now grabs the ExecProcess synchronously, awaits it for the Output, then enriches the resolved value with proc.aborted / proc.killed before captureResult runs.

#102: inputFile was read twice on the record path

buildCall reads inputFile to populate Call.stdin (for canonical matching). Real execa then re-reads the same file because we forwarded the original options. RunnerHooks.realCall gains a fourth parameter resolvedStdin: call.stdin on the record path, undefined on passthrough/no-session paths. The execa adapter swaps options.inputFile for input: resolvedStdin when both are present, so real execa consumes the resolved bytes instead of re-reading the file.

#128: _captureResultForTesting leaked into public sub-paths

The underscore-prefixed test export appeared in the published .d.ts for shell-cassette/execa and shell-cassette/tinyexec. Each adapter now imports captureResult from a sibling internal module (src/execa-capture.ts, src/tinyexec-capture.ts) that is not in package.json's exports map. Tests import the same path.

Schema and API

Schema stays additive. Cassettes without the killed field load and replay correctly via the synth fallback. Format stays at version 2.

RunnerHooks lives in src/wrapper.ts, which is not in the package's exports map, so the signature change (4th param) is internal.

Related Issues

Closes #126
Closes #128
Closes #129
Closes #102

Test Plan

• npm run lint
• npm run typecheck
• npm test (777 passing, 2 skipped)
• npm run build
• tests/integration/record-replay-aborted.test.ts extended to cover tinyexec
• tests/unit/execa-capture-result.test.ts and tinyexec-capture-result.test.ts cover the new killed field
• tests/integration/wrapper.test.ts covers synth fallback (legacy cassette without killed, new cassette with killed: false and signal: 'SIGTERM')
• tests/unit/wrapper-resolved-stdin.test.ts covers resolvedStdin threading on all five wrapper paths
• tests/unit/execa-input-file-swap.test.ts covers the execa adapter's inputFile -> input swap
• tests/unit/tinyexec-adapter.test.ts updated for the pre-await snapshot contract

Notes

tests/integration/record-replay-aborted.test.ts previously had a banner deferring tinyexec coverage to #126. That banner is removed; the file now covers both adapters.

The two tests in tests/unit/tinyexec-adapter.test.ts that asserted on aborted: true / killed: true were rewritten to mock the realistic shape: a Promise carrying the OutputApi fields as own properties, mirroring how real tinyexec exposes them. The previous mocks (flat object on mockResolvedValueOnce) implicitly tested the buggy path.