fix(re): the capture checker counted its own selftest fixture as a citation

`check-capture-citations` exits 1 on a clean checkout of this branch, and would
have kept doing so for ever:

    🔴 cited but NOT committed: 1
        docs/re/captures/no-such-file-anywhere.png

`SEARCH` includes `tools`, so the scan reads this file -- and `selftest()`'s
planted fixture is a literal capture path. The checker cited its own test data,
to a file that will never exist by construction. A gate that is red before
anyone changes anything teaches people to ignore it, which is the opposite of
what Phase 4 built it for.

Excluding only this one file (`SELF`) keeps every other tool in scope. A real
citation belongs in a page, or in a tool that opens the capture -- never in the
checker itself.

Added a selftest case for it, because this is exactly the class of bug the rest
of this file already documents surviving: the ERE that matched nothing while
five ticks stayed green. Verified the guard can fail, rather than assuming it:

    exclusion neutralised -> "own fixtures not counted 🔴 FAILED",
                             selftest rc=2, real check rc=1 reproducing the bug
    exclusion restored    -> selftest ok (7 cases), check rc=0

After the fix, on this branch:

    captures committed          : 212
      cited by a page or a tool : 212
      cited by nothing          : 0
      🔴 cited but NOT committed: 0        rc=0

which is also the first independent confirmation of Phase 4's "212 captures,
all cited" -- the checker now agrees with the page.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tools/re/check-capture-citations

@@ -41,6 +41,14 @@ CITE = re.compile(r"(?:docs/re/)?captures/[A-Za-z0-9._/-]+")
 CITE_ERE = r"(docs/re/)?captures/[A-Za-z0-9._/-]+"
 # Where a citation may live. Prose AND code: tests and tools open these files.
 SEARCH = ["docs", "crates", "tools", "port", "authored"]
+# 🔴 AND NOT THIS FILE. `SEARCH` includes `tools`, so the scan read *itself* --
+# and `selftest()`'s planted fixture below is a literal capture path. The check
+# therefore reported a dangling citation to a file that will never exist, and
+# exited 1 on a clean checkout, for ever. A gate that is red before anyone
+# changes anything teaches people to ignore it.
+# Excluding only this one file keeps every other tool in scope; a real citation
+# belongs in a page or a tool that opens the capture, never in the checker.
+SELF = ":!tools/re/check-capture-citations"
 
 
 def git(*args: str) -> str:
@@ -67,7 +75,7 @@ def committed() -> tuple[set[str], set[str]]:
 
 
 def cited() -> set[str]:
-    raw = git("grep", "-rhoE", CITE_ERE, "--", *SEARCH).splitlines()
+    raw = git("grep", "-rhoE", CITE_ERE, "--", *SEARCH, SELF).splitlines()
     out = set()
     for line in raw:
         c = line.split(":")[-1]
@@ -98,7 +106,7 @@ def named_bare() -> set[str]:
     out = set()
     for line in git("grep", "-rhoE",
                     r"[A-Za-z0-9._-]+\.(png|jpg|csv|log|txt|json|jsonl|bin|tsv)",
-                    "--", *SEARCH).splitlines():
+                    "--", *SEARCH, SELF).splitlines():
         out.add(line.split(":")[-1].strip())
     return out
 
@@ -151,7 +159,16 @@ def selftest() -> int:
     print("  %-34s %s  (%d citations found)"
           % ("citation gathering works", "ok" if gathering_ok else "🔴 FAILED", len(refs)))
 
-    ok = gathering_ok
+    # 🔴 REGRESSION GUARD FOR `SELF`. The planted fixture above is a literal
+    # capture path living in a file `SEARCH` covers. Before the exclusion
+    # existed the scan counted it as a real citation, so the check reported a
+    # dangling capture and exited 1 on a clean tree — permanently. If anyone
+    # drops `SELF`, this goes red here instead of in everybody else's run.
+    fixture_counted = cases[0][1] in refs
+    print("  %-34s %s"
+          % ("own fixtures not counted", "🔴 FAILED" if fixture_counted else "ok"))
+
+    ok = gathering_ok and not fixture_counted
     for name, path, want in cases:
         got = resolves(path.rstrip(".,;:)`"), files, dirs)
         mark = "ok" if got == want else "🔴 FAILED"