fix(agent): address gadfly — don't preamble-veto long answers; dedup ignores <url> wrappers

- isSubstantiveAnswer: restore the original "≥200 chars ⇒ real answer"
  unconditional accept (the preamble filter now applies only in the
  borderline 80–200 band). Applying preambleRe regardless of length regressed
  the recovery path: a long front-loaded answer opening with a conversational
  word ("Sure,", "Let me explain:", "First,") was wrongly discarded
  (flagged by glm-5.2 + claude-code/opus). The NVD-style planning-narration
  case is already handled by the citation-dominance check, not this filter.
- citations dedup: compare with <url> angle-bracket wrappers stripped, so a
  front-loaded turn that listed the same sources unwrapped still suppresses the
  duplicate block.
- doc: spell out the citationLabelRe leading class members (+ list markers);
  drop the stale "gated by preamble" note on recoverMinChars.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

agent/finalize.go

@@ -45,15 +45,26 @@ func finalOutput(msgs []llm.Message, terminal string) string {
 	}
 	if citations {
 		// Preserve the citations addendum below the recovered answer, unless the
-		// recovered turn already carries it verbatim (guards against a duplicate
-		// sources block when the front-loaded turn included its own citations).
-		if tail := strings.TrimSpace(terminal); !strings.Contains(rec, tail) {
+		// recovered turn already carries it (guards against a duplicate sources
+		// block when the front-loaded turn included its own citations). The
+		// containment test ignores <url> angle-bracket wrappers so a turn that
+		// listed the same sources unwrapped still suppresses the duplicate.
+		if tail := strings.TrimSpace(terminal); !strings.Contains(stripURLAngles(rec), stripURLAngles(tail)) {
 			return rec + "\n\n" + tail
 		}
 	}
 	return rec
 }
 
+// stripURLAngles removes the <…> wrappers Discord uses to suppress link embeds,
+// so the citations dedup compares URLs regardless of that formatting delta.
+func stripURLAngles(s string) string {
+	if !strings.ContainsAny(s, "<>") {
+		return s
+	}
+	return strings.NewReplacer("<", "", ">", "").Replace(s)
+}
+
 // backRefRe matches a terminal turn that merely points back to an earlier
 // message instead of stating the answer ("(Already answered above.)",
 // "see above", "as I said", ...).
@@ -66,11 +77,12 @@ var preambleRe = regexp.MustCompile(`(?i)^(let me|let'?s|i'?ll|i will|first[, ]|
 // citationLabelRe matches a terminal turn that OPENS with a sources/citations
 // heading — the shape a model produces when it front-loads its answer into an
 // earlier tool-call turn and closes with only its sources. Leading markdown
-// emphasis / list / block-quote / ATX-heading markers (with their whitespace,
-// via \s in the class) are tolerated before the label, and closing emphasis
-// (** / __) plus whitespace between the label and the colon/dash separator.
-// Anchored at ^ so a normal answer that merely mentions "sources" mid-sentence,
-// or ends with a "Sources:" section AFTER its prose, is never matched.
+// emphasis (*, _), list (-, +, *), block-quote (>), and ATX-heading (#) markers
+// — with their whitespace, since \s is in the class — are tolerated before the
+// label, as is closing emphasis (** / __) plus whitespace between the label and
+// the colon/dash separator. Anchored at ^ so a normal answer that merely
+// mentions "sources" mid-sentence, or ends with a "Sources:" section AFTER its
+// prose, is never matched.
 var citationLabelRe = regexp.MustCompile(`(?i)^[\s>#*_+-]*(sources?|references?|citations?|works cited|further reading)\b[\s*_]*[:：\-—]`)
 
 // linkRe matches a whole markdown link "[label](url)" or a bare URL. Used both
@@ -89,7 +101,8 @@ const (
 	// longer than this, so it is never treated as weak.
 	weakFinalMaxChars = 120
 	// recoverMinChars: a prior assistant turn this long is treated as a real
-	// answer regardless of how it opens (still gated by the preamble check).
+	// answer regardless of how it opens (the preamble filter is not applied at
+	// this length — see isSubstantiveAnswer).
 	recoverMinChars = 200
 	// recoverFloorChars / recoverRatio gate the borderline band: a shorter
 	// prior turn must clear the floor and — unless the terminal is a citations
@@ -164,20 +177,19 @@ func lastSubstantiveAssistantText(msgs []llm.Message, terminal string, citations
 // isSubstantiveAnswer reports whether txt (a prior assistant turn) reads like a
 // real answer rather than a preamble, relative to the terminal text.
 //
-// A preamble ("Let me look that up…") is never the answer regardless of length,
-// so that check applies BEFORE the length shortcut — otherwise a long planning
-// narration would be recovered. A sufficiently long non-preamble turn is
-// accepted; a shorter one must clear a floor and, unless the terminal is a
-// citations addendum (not a rival answer, so its length is irrelevant), also
+// A sufficiently long turn (>= recoverMinChars) is accepted unconditionally: a
+// multi-hundred-char turn is an answer even when it opens conversationally
+// ("Sure, here's…", "Let me explain: …"), so the preamble filter is NOT applied
+// to it — applying it there would drop a legitimate long front-loaded answer.
+// Only in the borderline band does a turn have to clear a floor, not read like a
+// short planning preamble ("Let me look that up…"), and — unless the terminal is
+// a citations addendum (not a rival answer, so its length is irrelevant) — also
 // clearly dwarf the terminal.
 func isSubstantiveAnswer(txt, terminal string, citations bool) bool {
-	if preambleRe.MatchString(txt) {
-		return false
-	}
 	if len(txt) >= recoverMinChars {
 		return true
 	}
-	if len(txt) < recoverFloorChars {
+	if len(txt) < recoverFloorChars || preambleRe.MatchString(txt) {
 		return false
 	}
 	return citations || len(txt) >= recoverRatio*len(terminal)