Document Notarius credential forwarding

docs/integrations/notarius.md

@@ -75,6 +75,27 @@ It does not pass a Narratio session ID or run `notarius config validate`
 automatically; the configured working directory and Narratio's minimal child
 environment apply to the subprocess.
 
+When `pipeline.notarius.llm_api_key` is absent or null, Narratio adds no
+credential to that environment. When configured, the field names an environment
+variable whose already-loaded nonempty value is forwarded under that exact
+name. Operators must use the same name as the `api_key_env` in the selected
+Notarius/PromptKit profile. Narratio does not inspect the Notarius configuration
+to infer a provider or destination name, and it does not forward unrelated
+credentials from its parent environment or secrets directory.
+
+The selected name is registered with Narratio's shared streaming redactor.
+Credential bytes written by the child to captured stdout, captured stderr, or
+stderr-derived failure diagnostics are replaced with `<redacted>`, including
+custom names not known to the built-in sensitive-name list. Narratio does not
+serialize the credential into arguments, stage metadata, manifests, or
+generated configuration.
+
+This captured-stream protection is not a filesystem sandbox. Notarius remains
+responsible for keeping credentials out of files it writes directly, including
+bundle artifacts and its own diagnostics. Narratio does not scan or rewrite
+arbitrary downstream files and cannot promise redaction of transformed or
+encoded credentials.
+
 ## Accepted Result
 
 Narratio's supported invocation baseline is Notarius v0.6.0. The accepted