* fix(vertex): report an unreadable credentials file as a read failure
Tell a path apart from inline JSON by shape, not os.path.exists().
Fixes#40166
* test(vertex): narrow pytest.raises to the expected message
* fix(vertex): log the credentials path instead of returning it to the caller
* refactor(vertex): log the credential source decision where it is made
* fix(vertex): handle paths open() rejects with a bare ValueError
* fix(vertex): redact the credentials path before it reaches the log
* test(vertex): cover the brace fallback and non-text credentials file
* test(vertex): exclude the unreachable exhaustiveness guard from coverage
* refactor(vertex): read the failure's fields off the matched object
CodeQL's py/uninitialized-local-variable does not follow keyword capture
patterns in a match statement and reported `path` and `reason` as possibly
unbound. Narrowing on the class and reading the attributes says the same thing
without a suppression.
* fix(vertex): accept a read-only mapping in extract_aws_params
* fix(vertex): keep encoded credentials out of the log and cover the legacy route
* fix(vertex): give one message for every credentials file failure and pick file or JSON by shape in Rust
* fix(vertex): read a `{`-named key file in Rust, name base64 there, and give one message when Google auth rejects a credentials file
* fix(vertex): read an unreadable `{`-named key file as a file, cap key file reads, and drop storage advice from the file message
* test(vertex): integration cells for credentials file and inline value failures
* test(vertex): drive the Rust messages cell through Vertex Claude
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Co-authored-by: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
VertexParams in auth-types holds the vertex_* fields of CredentialLiteLLMParams
in both spellings, with one ParamSpec per setting: the wire names, the litellm
module global VertexBase.get_vertex_ai_* consults, and the environment names.
A credential deserializes from text or the JSON object a config spells, an
empty object counts as absent, and both credential fields are redacted in
Debug. auth-gcp is split so lib.rs is the entrypoint (config, auth,
constants), its lookups resolve through the specs, secret_names() derives
from them, and get_vertex_ai_project_from_credentials reads a service
account's project_id for hosts that need it before a token exchange. The OCR
host folds the module globals in by spec at projection, so OcrSettings no
longer carries vertex_project and vertex_location.
