* fix(models): reuse the Claude Code OAuth token read from a file descriptor
ClaudeChatModel accepts a Claude Code OAuth token through
CLAUDE_CODE_OAUTH_TOKEN_FILE_DESCRIPTOR, but that handoff can be drained
only once: a pipe returns EOF after the first read and a file descriptor
keeps its advanced offset. _read_secret_from_file_descriptor read it again
on every call and kept nothing. Every ClaudeChatModel instance loads
credentials in model_post_init, and create_chat_model builds fresh
instances per run, so with a descriptor-only handoff the first model
authenticated and every model after it -- including the title model of
the very first run -- had no credential. The Anthropic SDK then raised
"Could not resolve authentication method" before sending a request.
A secret read from a descriptor is now kept for the life of the process,
keyed by (env_var, fd), so a different descriptor is still read fresh.
The read happens under a lock so two threads building their first model
concurrently cannot race one of them to EOF. Empty reads and OSError are
not cached and behave as before; lookup order, config keys, and log
messages are unchanged.
* docs(changelog): reference #5411 in the Claude Code OAuth descriptor fix entry
* test(models): pin that a closed descriptor handoff keeps its token
Review follow-up on #5411: the descriptor secret cache is keyed on the
fd number, which the OS recycles. Folding os.fstat identity into the key
would break the property the cache exists for -- once the handoff fd is
closed after the first read, fstat raises EBADF and every later model
would lose the token again -- and it would still miss a regular file
rewritten in place, which keeps its st_dev/st_ino.
The handoff is fixed at process start, so keep the number as the key and
state the invariant instead: a closed handoff keeps serving its token, a
secret placed on a recycled number is not re-read, and anything handing
over a new secret in-process must clear the cache. A new test pins the
closed-handoff behavior; an fstat-fingerprinted key fails exactly that
test.
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