migrate-rollouts reports nonempty legacy flat rollout files as empty (invalid_session_metadata)

Finding: In one external report against codex-cli 0.162.1 (official Homebrew install, Darwin arm64), 22 legacy flat-format rollout files from 2025 were reported by codex migrate-rollouts as empty, although the reporter says the files have content. Doctor also reported scan errors for rollouts with no usable header record. Source: https://github.com/openai/codex/issues/52904. This is an external report only; KFA did not reproduce it. Reported details: The reporter says all 22 files pass line-by-line JSON parsing and that file size is above zero (the repro steps specify checking that each nonempty line is valid JSON and that size is greater than zero). The first record has id, timestamp and instructions fields, and later records hold response items directly, without the session_meta/payload wrapper. The files total 15,967,874 bytes. The reporter says three contain only metadata and 19 contain subsequent records (https://github.com/openai/codex/issues/52904). Observed behavior: codex doctor --json showed state.rollout_db_parity as a warning with 22 rollout DB scan errors, 0 malformed file names, scan cap not reached and 0 stale rows. The reported scan error text was: rollout at <redacted-path> has no usable header record. The source does not give a per-file mapping of these errors to the 22 files. The reporter says they ran codex migrate-rollouts --json restricted to the 22 thread IDs, without --apply (the repro steps give the form codex migrate-rollouts --thread <thread-id> --json). All 22 entries returned status failed, failure_reason invalid_session_metadata and bytes_processed 0. The reported message was: rollout at <redacted-path> is empty (https://github.com/openai/codex/issues/52904). Interpretation, which is a hypothesis rather than confirmed cause: the reporter's evidence suggests the migration path does not recognize the legacy flat header, and the empty-file wording misdescribes a format-recognition failure. No maintainer has confirmed this. The reporter linked the v0.162.1 source files thread_inventory.rs, rollout_migration.rs and line_parser.rs as relevant, but the supplied content does not include any analysis of them. Expected behavior per the reporter: distinguish empty files from unsupported legacy formats with an accurate message. If the format is in scope, provide an official migration path that preserves the content. Status: The issue is open. The supplied sources show no maintainer response, workaround, fix commit or released fix. Whether the legacy flat format is meant to be supported is unknown. Only runs without --apply were reported; results of any --apply attempt were not reported. The reporter states the original files remain unchanged.