feat(cpg): give the files a frontend refuses a CPG of their own

A dropped file is dropped from the ONLY graph there is, so every question
about it has no answer -- which is how a 637-file plugin became a scan of
nothing. But those files build perfectly well alone: the failure is
per-invocation, not per-file. So a file the main build refuses is excluded
from it, given a second CPG, and both are queried with rows concatenated per
request id.

    pmpro two-file slice   before: cpg_empty, 0 findings
                           after:  18 entailed incl. CVE-2023-23488 at :936,
                                   reported with cpg_sharded

What this does NOT buy is a flow that crosses the shard boundary: a source in
the excluded file whose sink is in the rest of the tree is invisible to every
question asked, and no merging of results recovers it. That is why the split
is REPORTED rather than quietly served as if it were whole.

The excluded-file tree is symlinks at the original relative paths. A region
asks about `classes/class.memberorder.php` and the queries match a filename by
suffix, so a flattened copy would cheerfully answer about a file nobody asked
about.

Reports gain "What could not be analysed", rendering cpg_sharded, cpg_empty,
files_unparsed, query_failed and budget_exhausted in the reader's terms. A
degradation is a fact about coverage, not a warning to file away: silence in
the coverage table means "no fact table covered this", and silence about an
empty or split graph means something else entirely.

Also removes the WordPress vocabulary from the query, which was the other half
of this request. `apply_filters` was a hardcoded Set in taint.sc and
`add_action|add_filter|add_shortcode` a hardcoded alternation in mapping.py.
Both are now a `[[dispatch]]` fact:

    [[dispatch]]
    id = "wordpress_hooks"
    register = ["add_action", "add_filter", "add_shortcode"]
    apply = ["apply_filters", ..., "do_action", ...]

The shape is general -- a registry keyed by a string literal at both ends, as
Django signals, jQuery events and Symfony's dispatcher all are -- so a second
framework is a row in a TOML rather than an edit to a query. `dispatch_apply`
is empty for every language that declares none, and the hook half then does
nothing at all rather than looking for names that mean nothing there.

848 tests pass; gates byte-identical. wpstatistics 3/2 with the CVE at :225 on
the vulnerable side only, mwwpform 1/0, pmpro 18/1, VAmPI 4 unchanged.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01T7XD7x5KonMdmGRkp63EQG

.kiro/specs/contributor-scan/tasks.md

@@ -596,8 +596,20 @@
     (`_build_with_retries`, 4 attempts). Retrying is only sound because the failure is intermittent AND
     reported -- retrying a silent failure would be superstition. Driver-level result on the slice that
     previously needed four manual retries: **6 of 6 builds usable**, 3 entailed findings each time.
-  - Still open: a file that fails on every attempt is still reported rather than analysed, and `--exclude`
-    plus a second CPG for the excluded files is the remaining lever.
+  - **Excluded files now get a CPG of their own, 2026-09-10.** A file the frontend refuses is excluded from
+    the main build and put in a second graph -- the same file builds perfectly well alone, the failure being
+    per-invocation -- and the queries run over both, rows concatenated per request id. The two-file PMPro
+    slice that used to report `cpg_empty` and nothing at all now reports **18 entailed findings including
+    CVE-2023-23488 at :936**, with `cpg_sharded` beside them.
+  - What it does NOT buy is a flow that crosses the shard boundary, and that is why the split is reported
+    rather than quietly served: a source in the excluded file whose sink is in the rest of the tree is
+    invisible to every question asked. `reports` now renders this under "What could not be analysed", along
+    with `cpg_empty`, `files_unparsed`, `query_failed` and `budget_exhausted` -- a degradation is a fact
+    about coverage, not a warning to file away.
+  - The excluded-file tree is symlinks at the ORIGINAL relative paths, because a region asks about
+    `classes/class.memberorder.php` and the queries match a filename by suffix; a flattened copy would answer
+    about a file nobody asked about.
+  - Still open: nothing here recovers a cross-shard flow, and the 637-file build remains unmeasured.
   - Still open: wiring that exclusion loop, the 637-file build with it in place, and whether the REST handler
     two calls away can reach the sink -- the slice found it through a same-function flow, not across the
     object.