fix(runtime): exit 77 when collected data cannot be written for lack of disk

[gastonyelmini]

Problem

An integration that fills its volume currently finishes with exit code 0.

Every graph object collected is written to disk before upload, so ENOSPC there is unrecoverable — but it propagates as an ordinary error. flushDataToDisk logs Failed to write chunk to disk and rethrows, the step executor marks that one step failed and moves on to the next, which fails the same way, and the job ends "with errors" having exited cleanly.

For managed integrations that clean exit is the whole problem. The ECS state machine only reaches HandleTaskFailure when the task itself fails, so a task that ran the disk dry is never retried on a larger volume and the disk-scaling path in jupiter-integration-service can never fire. It also publishes a partial graph, which looks to the customer like their data disappeared rather than like a failed run.

Real example: integration job fc815601-295c-42d8-acd8-302b49e267c5 hit ENOSPC, exited 0, and handle-task-failure never ran — no lambda logs exist for that task.

Change

writeFileToPath and symlink — the two calls flushDataToDisk makes, and therefore the funnel every graph object write passes through — detect ENOSPC and exit with code 77, which handleTaskFailure already reads as "retry this task with a bigger disk". Every other error keeps behaving exactly as before.

The diagnostic is written to fd 2 with writeSync because process.exit does not flush pending async writes, and that line is the only record of why the task died.

Notes for review

• This is the first process.exit in the SDK's production code. The local j1-integration CLI shares this path, where the effect is that filling the disk stops the run instead of producing a confusing stack trace.
• OUT_OF_DISK_EXIT_CODE is exported and covered by a test, because the value is a contract with a separately deployed service.

Testing

8 new tests in src/__tests__/fileSystem.test.ts covering the write, mkdir, symlink and JSON paths, the stderr diagnostic, an unwritable stderr, and the non-ENOSPC passthrough. Full integration-sdk-runtime suite green (301/301).