fix(steward): route on the declared DELEGATE line, not on prose

The prompt tells the Steward to state its choice on a DELEGATE line and
to explain itself on REASON, COMPLEXITY and CONTEXT lines. Extraction
ignored that structure and substring-matched capability domains across
the entire response, so ordinary English in the explanation selected
agents: "description" contains the housekeeper domain "script",
"discover" contains "cover", "acknowledge" contains "knowledge" and
"know", "economy" contains the biographer domain "my".

Every one of those was a real delegation. A spurious librarian is a
multi-second web call on a query that asked for arithmetic.

It also made prose length a routing input, which would have quietly
corrupted the thinking benchmark this was found during: anything that
shortened the Steward's output reduces accidental substring hits and so
reads as improved routing.

Resolution is now layered, most explicit first — a DELEGATE line opening
with a capability name, then a capability named anywhere on that line,
then a domain on that line. With no DELEGATE line at all the response is
matched on capability names only, never domains, so the conversational
path still answers with no capabilities. Matching is whole-word
throughout.

Co-Authored-By: Claude <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Steward routing no longer triggers on words inside its own explanation. Capability
+  extraction reads the declared `DELEGATE:` line instead of substring-matching
+  capability domains across the whole response, where ordinary English routed
+  requests — "description" contains the housekeeper domain "script", "acknowledge"
+  contains "knowledge" and "know". A spurious capability meant a real agent call,
+  including web searches, on queries that needed none.
+
 ## [2.4.2] - 2026-07-19
 
 ### Fixed