Clarify collection contracts and migration docs

docs/internal/observation.md

@@ -23,6 +23,10 @@ callback. The caller supplies normalized failure metadata; the recorder never
 parses an error string or receives provider bodies, credentials, headers, or
 other content. Events are values with no mutable containers. Callback panics
 propagate to the caller.
+Resolved prompt and profile IDs are the exact runtime identities selected for
+the invocation, including namespace qualification when supplied by an engine
+view. A prompt's optional version label is descriptive metadata, not a
+selection key.
 Per-operation callbacks are ordered and synchronous; different operations may
 invoke the same callback concurrently. The recorder marks each measured phase's
 end before delivery, so callback work does not inflate provider duration.