* fix(config): close out #4124 review follow-ups
Extracts the (mtime, size, sha256) content-signature helper that was
duplicated between config/app_config.py and mcp/cache.py into a new
config/file_signature.py, and fixes ExtensionsConfig.resolve_config_path()
to return None instead of raising FileNotFoundError when an explicit
config_path argument or DEER_FLOW_EXTENSIONS_CONFIG_PATH points at a file
that has since been deleted -- the exact resolution mode Docker dev/prod
uses per AGENTS.md, so the MCP tools-cache staleness check could raise
instead of degrading to "not stale". Both were flagged by willem-bd in
review on #4124 and explicitly deferred there ("flagging for visibility",
"leaving the extraction as the follow-up you suggested").
* fix(config): keep explicit extensions-config paths fail-loud
resolve_config_path() previously turned every missing-file case into a
clean None, including an explicit config_path argument or
DEER_FLOW_EXTENSIONS_CONFIG_PATH (the exact mode Docker dev/prod uses).
That silently downgrades a bad Docker mount, typo, or deleted
production config to "no extensions" instead of surfacing the
misconfiguration, per fancyboi999's review [P1] and willem-bd's
follow-up notes on this PR.
Restores FileNotFoundError for the two explicit modes (config_path
argument, DEER_FLOW_EXTENSIONS_CONFIG_PATH); only the fallback search
mode (no explicit path/env var, nothing found in the usual locations)
still returns None, since that is the legitimate "extensions were
never configured" case.
The one caller that needs the old fail-soft behavior -- the MCP
tools-cache staleness check, which re-resolves the path on every
get_cached_mcp_tools() call -- gets a narrow, local catch instead
(deerflow.mcp.cache._resolve_config_path) so a config file going
missing mid-run still degrades the cache to "not stale" rather than
crashing a hot per-request path. Also hoists the double os.getenv()
read in the env-var branch into a local, per willem-bd's nit.
Adds resolver-level tests for both explicit-path and env-var raises,
a dedicated search-mode None regression test, and updates the
existing MCP-cache docstrings to describe the corrected split.
