refactor(bin): retrofit research to the ADR-0020 context contract

Description 583 -> 231 chars and body 854 -> 519 words. Deletes the
neuledge-context boundary clause outright: commit 6146120 deleted that
skill and no skill has owned MCP-server installation since. That was the
last dangling routing target in the corpus.

Removes META.md, which file-structure.md:20 forbids at a skill root. Its
when: field duplicated the description and its references: entry pointed
at .agents/skills/context7-mcp/SKILL.md, which does not exist.

Restores two rules a clean-context audit found had lost their force: the
starting-URLs branch in step 3, which the retrofit had reduced to a
condition with no behaviour, and the references/file-format.md pointer at
step 6. The second matters downstream -- validate-provenance.sh parses
sources.md with anchored regexes and check 8 short-circuits silently when
the Status field is absent, so a sources.md written from step 6 alone
broke the provenance chain with no error anywhere.

Rewrites steps 4-5 as serial WebFetch reads. They mandated spawning
subagents that allowed-tools never granted; no tool was added because the
name differs across the three compile targets. Tracked as #116.

Updates the two test pins and the eval case that asserted the dead route.

Refs #99

tests/test-skill-size-check.sh

@@ -534,10 +534,12 @@ expect_gate "a fixture with no authoring root reports DID NOT RUN and exits 0" \
     "Use when doing the thing. Do not use for improvements — use some-other-skill instead." 10)" \
   "Unchecked target(s): some-other-skill"
 
-echo ""
-echo "--- the live dangling routing targets are caught (issue #100) ---"
+# NOTE: this section prints no header and runs no assertions any more — see why
+# below. The commentary is kept because it records why probes are removed rather
+# than skipped, which is the rule the next person to touch this file needs.
+#
 # ADR-0020 records the broken routing targets and splits fixing them into its own
-# issue. This asserts the gate actually sees them rather than the check being
+# issue. This asserted the gate actually sees them rather than the check being
 # vacuous in the corpus it was written against.
 #
 # There used to be a third probe here, for `skill-improve` in skill-audit's
@@ -556,29 +558,26 @@ echo "--- the live dangling routing targets are caught (issue #100) ---"
 # The gitea-labels probe was dropped when the issue #99 retrofit cut the
 # composition sentence whose YAML fold produced that target. Per the rule above
 # it is removed, not skipped.
-# shellcheck disable=SC2043  # one probe left by design -- the list shrinks as
-# each fixture is retrofitted and reaches zero when `research` lands. Keeping the
-# loop means removing the last entry is a one-line edit, not a restructure.
-for probe in \
-  "plugins/bin/.apm/skills/research/SKILL.md:neuledge-context"; do
-  probe_file="$REPO_ROOT/${probe%%:*}"
-  probe_name="${probe##*:}"
-  if [[ ! -f "$probe_file" ]]; then
-    fail "the probe fixture ${probe%%:*} no longer exists — this pin has become vacuous; update it and EXPECTED_DANGLING in tests/test-adr0020-targets.sh together"
-    continue
-  fi
-  # Captured, not piped: the script exits non-zero on these files and
-  # `set -o pipefail` would make the whole pipeline non-zero regardless of what
-  # grep found.
-  set +e
-  probe_out="$("$SCRIPT" "$probe_file" 2>&1)"
-  set -e
-  if [[ "$probe_out" == *"routes to '$probe_name'"* ]]; then
-    pass "detects the dangling '$probe_name' target in ${probe%%:*}"
-  else
-    fail "did not detect the dangling '$probe_name' target in ${probe%%:*}. If issue #100 retrofitted it, drop this probe and update EXPECTED_DANGLING in tests/test-adr0020-targets.sh; if a false-positive fix took a true positive with it, that is the regression this asserts."
-  fi
-done
+#
+# The `neuledge-context` probe — the last one — went the same way in wave 3 of
+# that retrofit, which deleted the boundary clause naming it. **The corpus now
+# has zero dangling targets**, so this loop is removed entirely rather than left
+# to iterate over an empty list.
+#
+# That is deliberate and follows the rule stated above. A loop over no probes
+# produces no assertion while still returning success, which is the vacuous-pass
+# shape this comment block exists to reject — it would make the suite look one
+# test stronger than it is, exactly the complaint levelled at the old
+# `skill-improve` SKIP branch.
+#
+# Nothing is lost. This file only ever checked that each member of the live
+# dangling set is individually detected; tests/test-adr0020-targets.sh remains
+# the authority on the set itself, and now pins it as EMPTY, which is what
+# catches a newly-authored clause naming a target that does not resolve. That
+# file also carries synthetic fixtures built inside a real plugin tree, which
+# exercise the detection path without depending on the corpus staying broken.
+#
+# If a real dangling target ever reappears, add its probe back here.
 
 echo ""
 echo "Results: $PASS passed, $FAIL failed"