fix(agent): "In short supply" is not a short version

Round 5. Two of the eight findings are the em-dash mid-rune slice, which
the orientation matrix had already caught and fixed in 285789c before
this round returned — the harness doing the reviewers' job, which is the
point of it.

Of the rest:

**A marker phrase can open a sentence and still be prose** (kimi).
"That's the chain above. In short supply of alternatives, we went with
B." opens a sentence with "In short" and announces nothing. The marker
must now be followed by the delimiter a model puts after a real
announcement — the colon in "Short version:", the comma in "In short,".
No delimiter means no match, which keeps the terminal: fails closed.

Adding that made the sentence-opening anchor look redundant — a
break-check that removed it survived, because every mid-sentence case in
the table was by then rejected for want of a delimiter. It is not
redundant: "…, and in short, we went with B" is a clause continuation
with a comma. The missing thing was a case for what the anchor alone
does, not the anchor.

**backRefHeadChars was named for the wrong family** (opus; sonnet raised
the same constant from the other side). It is applied only to the
deictic offset test, never to backRefRe. Renamed abovePointerHeadChars.
It stays defined as `= weakFinalMaxChars` rather than inlined, because an
earlier round asked for exactly that linkage and the reason still holds.

**The clause-boundary comment narrated my review history** (opus) — the
same class of finding I took two rounds ago and then reintroduced one
comment over. Rewritten as behaviour, pointing at the matrix.

**analysis1611 was a function returning a constant string** (sonnet) —
now a var.

Accepted, not fixed: a comparative "above," plus a sentence-opening
marker can still reach isSummaryCloser. That needs the comparative false
positive, a real marker, a terminal under 300 bytes, and a same-turn
prior at least 3x longer, all at once; the dwarf ratio is the backstop
and no lexical test separates the comparative from the deictic.

Break-check: seventeen mutations, each killed by a named test.

agent/finalize.go

@@ -161,7 +161,7 @@ func pointsAbove(t string) bool { return aboveRefLoc(t) != nil }
 // bareAbovePointer cannot disagree about what counts as a pointer.
 func aboveRefLoc(t string) []int {
 	loc := aboveRefRe.FindStringIndex(t)
-	if loc == nil || loc[0] > backRefHeadChars {
+	if loc == nil || loc[0] > abovePointerHeadChars {
 		return nil
 	}
 	return loc
@@ -204,12 +204,11 @@ func bareAbovePointer(t string) bool {
 
 // clauseBoundaryChars ends the clause the reference belongs to. Commas,
 // semicolons, colons and dashes are in it, not just sentence terminators,
-// because the answer can share the reference's SENTENCE: "Ship Tuesday, as
-// shown above." is a decision plus a pointer, and cutting back only to the
-// previous full stop swallowed the decision and made the whole thing look
-// bare. That is the same defect as treating a pointer as disposable because
-// something followed it — mirrored, and it survived a round of review because
-// every case I had written put the answer AFTER the pointer.
+// because the answer can share the reference's SENTENCE — "Ship Tuesday, as
+// shown above." is a decision plus a pointer, and cutting back to the previous
+// full stop would swallow the decision and make the whole terminal look bare.
+// Content on either side of the pointer disqualifies it equally; see
+// TestBareAbovePointerOrientations, which checks every placement.
 const clauseBoundaryChars = ".!?\n,;:—"
 
 // pointerResidueCutset is trimmed from both ends of what survives cutting the
@@ -238,12 +237,22 @@ var bareRemainderRe = regexp.MustCompile(`(?i)^(` + fillerWords + fillerSep + `*
 // comment explains: a user who asked for brevity is answered with exactly that
 // shape.
 //
-// The marker must OPEN a sentence. Mid-sentence the same words are ordinary
-// prose carrying new content — "Given the analysis above, the bottom line is
-// that we need a different vendor" states a conclusion, it does not announce a
-// condensation — and treating that as disposable is the very failure the
-// two-part test exists to prevent.
-var compressionMarkerRe = regexp.MustCompile(`(?i)(^|[.!?:;—]\s*|\n\s*)(short version|shorter version|short answer|tl;?dr|in short|in brief|in summary|in sum|bottom line|net[- ]net|the gist)\b`)
+// The marker must OPEN a sentence AND be followed by a delimiter — the colon
+// or comma a model puts after it when it is genuinely introducing the short
+// form. Both halves are needed against a different failure each:
+//
+//   - Mid-sentence the same words are ordinary prose carrying new content.
+//     "Given the analysis above, the bottom line is that we need a different
+//     vendor" states a conclusion; it does not announce a condensation.
+//   - At a sentence opening the words can still run on into ordinary prose.
+//     "In short supply of alternatives, we went with B" opens a sentence with
+//     "In short" and is not a summary at all.
+//
+// A marker with no delimiter ("In short we chose B") is not matched, which
+// fails closed: the terminal is kept, which is today's behaviour.
+var compressionMarkerRe = regexp.MustCompile(`(?i)(^|[.!?:;—]\s*|\n\s*)` +
+	`(short version|shorter version|short answer|tl;?dr|in short|in brief|in summary|in sum|bottom line|net[- ]net|the gist)` +
+	`\s*([:,—-]|$)`)
 
 // summaryCloserRe matches a terminal turn that OPENS with a bookkeeping
 // acknowledgment of the citation round — "Citations are logged.", "Sources
@@ -319,15 +328,19 @@ const (
 	// genuine final answer that merely contains "as I said" mid-sentence is
 	// longer than this, so it is never treated as weak.
 	weakFinalMaxChars = 120
-	// backRefHeadChars bounds how far into the terminal a deictic "above" may
-	// sit and still read as pointing OUTSIDE this message (see pointsAbove).
-	// It IS weakFinalMaxChars — the same guard ("there is not enough text
+	// abovePointerHeadChars bounds how far into the terminal a deictic "above"
+	// may sit and still read as pointing OUTSIDE this message (see
+	// pointsAbove). It applies to the deictic family only — backRefRe's fixed
+	// phrases are matched anywhere under the weak cap — so it is named for the
+	// pointer, not for the back-reference family as a whole.
+	//
+	// It IS weakFinalMaxChars: the same guard ("there is not enough text
 	// before the reference for it to be pointing at content inside this
 	// turn"), expressed as an offset because a summary closer carries a
 	// compression AFTER the pointer and so is not itself short. Defined by
-	// reference, not by repeating the literal: tuning the weak cap without the
-	// offset following it would split one rule into two.
-	backRefHeadChars = weakFinalMaxChars
+	// reference rather than by repeating the literal, because tuning the weak
+	// cap without the offset following it would split one rule into two.
+	abovePointerHeadChars = weakFinalMaxChars
 	// recoverMinChars: a prior assistant turn this long is treated as a real
 	// answer regardless of how it opens (the preamble filter is not applied at
 	// this length — see isSubstantiveAnswer).