server.close() only stops new connections; an in-flight fire-and-forget
cache save can land a file mid-recursive-rm, surfacing as ENOTEMPTY on
slower runners (run #5). fs.rm's built-in retries absorb the window.
`codeburn context <session>` accepts an 8-char session id prefix (findClaudeSession/
findCodexSession resolve it via startsWith), but /api/context/tree additionally
required the resolved ref's sessionId to equal the id passed in verbatim - so
the same prefix that works on the CLI 404s through the API.
findClaudeSession/findCodexSession are already the single source of truth for
prefix resolution used by the CLI; the API now trusts that resolution instead
of re-validating for an exact match afterwards, so both surfaces behave the
same way for a prefix.
Fixesgetagentseal/codeburn#767 (item 2).
