Convert old Session logs into Session traces #993

Parent

#700

What to build

A one-time logs option converts every Session log under the machine's logs folder into a Session trace beside it, Security runs' included, using the same code that writes Session traces live.

• Estimated times: a record without a time of its own gets one estimated from the Command log, as the Waterfall estimates times now, and is marked as estimated.
• Codex diffs: old Codex sessions get their diffs where Codex's session files still exist (Codex's diffs from its own session file #988).
• The round-trip report: for each session, it compares what the conversation view, the Waterfall, show and Model evidence read from the original and from its Session trace.
• The originals stay until a second step, run after reading the report, removes them. It removes only those whose conversion passed.

Acceptance criteria

• Integration tests convert Session-log fixtures for all six Harnesses, and the round-trip report shows no difference for any of them.
• Estimated times are marked as estimated, and Codex diffs are added when the fake Codex file exists.
• Running it again converts nothing twice.
• The removal step removes only originals whose conversion passed.
• The guide says how to run both steps.