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

src/openultrasast/model/scan.py

@@ -190,6 +190,13 @@ def scan_repository(
                     methods = int(str(entry.get("methods", "0")) or 0)
                     if methods == 0:
                         degradations.append({"stage": "model", "reason": "cpg_empty", "files": int(str(entry.get("files", "0")) or 0)})
+                    # More than one graph means some files could only be built apart from the rest, and a
+                    # flow whose source is in one shard and whose sink is in another does not exist for any
+                    # question we can ask. Reporting the split is the difference between a partial answer and
+                    # a partial answer that looks whole.
+                    shards = int(str(entry.get("shards", "1")) or 1)
+                    if shards > 1:
+                        degradations.append({"stage": "model", "reason": "cpg_sharded", "shards": shards})
                     census_reported = True
                 rows_by_id.update(answered_batch)
         else:  # a backend without batching still works, one call at a time

src/openultrasast/model/specs.py

@@ -112,6 +112,9 @@ class TaintSpec:
     # discharge is a guard and not a call.
     bounded_sinks: tuple[str, ...] = ()
     safe_shape_sinks: tuple[str, ...] = ()
+    # The calls that read a value back out of a string-keyed registry (`apply_filters`, `do_action`). Facts,
+    # not constants, so a second framework is a row in a TOML rather than an edit to the query.
+    dispatch_apply: tuple[str, ...] = ()
 
 
 @dataclass(frozen=True)
@@ -221,6 +224,7 @@ def taint_specs(
     def _is_shape(fact: object) -> bool:
         return bool(getattr(fact, "parameterized", False)) or getattr(fact, "literal_format_arg", None) is not None
 
+    dispatch_apply = tuple(sorted({call for fact in scoped.dispatches for call in fact.apply}))
     sanitizers = tuple(sorted({call for fact in scoped.sanitizers if not _is_shape(fact) for call in fact.calls}))
     safe_shapes = tuple(sorted({call for fact in scoped.sanitizers if _is_shape(fact) for call in fact.calls}))
     by_family: dict[str, set[str]] = {}
@@ -243,6 +247,7 @@ def taint_specs(
             sanitizers=sanitizers,
             bounded_sinks=tuple(sorted(bounded.get(family_id, ()))),
             safe_shape_sinks=safe_shapes,
+            dispatch_apply=dispatch_apply,
         )
         for family_id, calls in sorted(by_family.items())
     }

src/openultrasast/model/taint.py

@@ -51,6 +51,9 @@ def request_params(
         # graph, because php2cpg drops a registration's callback argument entirely -- see
         # `mapping.php_hook_callbacks`. Empty for every language that does not register handlers by string.
         "hookCallbacks": hook_callbacks,
+        # The registry's own vocabulary, from the fact tables. Without it the query would have to know what
+        # `apply_filters` is, which makes a general mechanism into a WordPress feature.
+        "dispatchApply": spec.dispatch_apply,
     }