fix(call-path): keep caller-only unknown coverage from blocking not_found (#2371)

* fix(call-path): keep caller-only unknown coverage from blocking not_found

build_call_path expands only callee edges, so relationship coverage that
is unknown solely because callers are unobservable (the modern headless
IDA profile) no longer marks the searched callee closure incomplete.
The caller caveat stays visible in limitations, and callee-side unknowns
still yield unknown. Fixes #2322.

* test(call-path): cover IDA-capped callees beside unknown callers

Greptile review noted the poll-timing coverage only exercised unknown
callees, leaving the partial callees IDA returns at its 500-result cap
untested. Add the combined unknown-callers/partial-callees case:
isCallerOnlyUnknownCoverage must stay false and buildCallPath must keep
search_scope.exhaustive false, so a future change cannot silently report
not_found when IDA has omitted callees.

src/domain/functionCallCoverage.ts

@@ -2,6 +2,9 @@ import type { RelationshipCoverage } from "./relationshipCoverage.js";
 import type { FunctionDossier } from "./hopperValues.js";
 import { uniqueSorted } from "./canonicalOrdering.js";
 
+const callerCoveragePrefix = "Callers: ";
+const calleeCoveragePrefix = "Callees: ";
+
 /** Combine caller and callee read outcomes without losing either explanation. */
 export const combineFunctionRelationshipCoverage = (
   callers: RelationshipCoverage | undefined,
@@ -20,7 +23,8 @@ export const combineFunctionRelationshipCoverage = (
   );
   const details = diagnostics.length > 0 ? { diagnostics } : {};
   const reasons = reads.flatMap(({ direction, coverage }) => {
-    const label = direction === "callers" ? "Callers" : "Callees";
+    const label =
+      direction === "callers" ? callerCoveragePrefix : calleeCoveragePrefix;
     const limitations =
       coverage === undefined
         ? ["Provider did not report relationship coverage."]
@@ -29,7 +33,7 @@ export const combineFunctionRelationshipCoverage = (
           : coverage.status === "partial"
             ? coverage.limitations
             : [];
-    return limitations.map((reason) => `${label}: ${reason}`);
+    return limitations.map((reason) => `${label}${reason}`);
   });
   if (
     reads.some(
@@ -50,6 +54,20 @@ export const combineFunctionRelationshipCoverage = (
   return { status: "complete", ...details };
 };
 
+/**
+ * Whether combined relationship coverage is unknown only on the caller side.
+ * The combine helper above prefixes each direction's reasons, so a reason
+ * that carries the caller prefix and no callee prefix records observed
+ * callees with unobservable callers. Forward (callee-edge) searches stay
+ * exhaustive under that caveat; the caller reason remains a limitation.
+ */
+export const isCallerOnlyUnknownCoverage = (
+  coverage: RelationshipCoverage,
+): boolean =>
+  coverage.status === "unknown" &&
+  coverage.reason.startsWith(callerCoveragePrefix) &&
+  !coverage.reason.includes(calleeCoveragePrefix);
+
 /** Explain why two resolved call sets cannot establish call-set equality. */
 export const functionCallCoverageLimitations = (
   coverage: RelationshipCoverage | null,