diff --git a/src/ghidra/GhidraProjectSnapshot.ts b/src/ghidra/GhidraProjectSnapshot.ts
index 64105951db..75f85566e6 100644
--- a/src/ghidra/GhidraProjectSnapshot.ts
+++ b/src/ghidra/GhidraProjectSnapshot.ts
@@ -24,6 +24,7 @@ import {
 } from "../filesystem/RegularFile.js";
 import { ConfigurationError } from "../domain/configurationErrors.js";
 import { compareUnicodeCodePoints } from "../domain/unicodeCodePointOrder.js";
+import type { JsonValue } from "../domain/jsonValue.js";
 import type { GhidraProjectSelection } from "../config/ghidraExistingProject.js";
 import { ghidraProgramNameSchema } from "../config/ghidraExistingProject.js";
 
@@ -59,9 +60,11 @@ export type GhidraProjectCommitment = z.infer<
 const selectionFailure = (
   message: string,
   setting = "REA_GHIDRA_PROJECT_PATH",
+  diagnostics?: Readonly<Record<string, JsonValue>>,
 ): ConfigurationError =>
   new ConfigurationError(message, {
     settings: [{ setting, constraint: message }],
+    ...(diagnostics === undefined ? {} : { diagnostics }),
   });
 const entriesFor = (name: string) => [`${name}.gpr`, `${name}.rep`] as const;
 
@@ -176,7 +179,14 @@ export const resolveGhidraProject = async (
       // Admit the caller's exact marker before canonicalizing its parent.
       // Darwin realpath(file/..) can succeed despite native lookup rejecting
       // that traversal; hashing the canonical sibling would select a new input.
-      if (!(await lstat(selection.path)).isFile())
+      const marker = await lstat(selection.path).catch(absentProjectEntry);
+      if (marker === undefined)
+        throw selectionFailure(
+          `Existing Ghidra project marker does not exist: ${selection.path}`,
+          "REA_GHIDRA_PROJECT_PATH",
+          { system_code: "ENOENT", syscall: "lstat" },
+        );
+      if (!marker.isFile())
         throw selectionFailure(
           `Existing Ghidra project marker must be a regular file: ${selection.path}`,
         );
diff --git a/src/ghidra/GhidraProvider.behavior.test.ts b/src/ghidra/GhidraProvider.behavior.test.ts
index 911f280a7b..3c70f66f5c 100644
--- a/src/ghidra/GhidraProvider.behavior.test.ts
+++ b/src/ghidra/GhidraProvider.behavior.test.ts
@@ -4620,6 +4620,26 @@ it("reports every Windows existing-project capability unavailable before open",
   }
 });
 
+it("reports an unsupported existing-project target as an invalid REA_GHIDRA_PROJECT_PATH setting", async () => {
+  const ghidra = provider(installationHost(), undefined, {
+    REA_GHIDRA_PROJECT_PATH: join(process.cwd(), "selected.gpr"),
+  });
+  try {
+    const resolved = await ghidra.resolveAnalysisProfile({
+      ...executableTarget("elf", "x86_64"),
+      format: "dos-com",
+    } as unknown as BinaryTarget);
+    expect(resolved.ok).toBe(false);
+    if (resolved.ok) return;
+    expect(resolved.error).toMatchObject({
+      _tag: "ConfigurationError",
+      settings: [{ setting: "REA_GHIDRA_PROJECT_PATH" }],
+    });
+  } finally {
+    await ghidra.closeOwnedResources();
+  }
+});
+
 it("keeps saved project reports as shared historical Evidence without applying fresh overrides", async () => {
   const root = await mkdtemp(join(tmpdir(), "rea-history-project-"));
   await mkdir(join(root, "history.rep"));
diff --git a/src/ghidra/GhidraProvider.ts b/src/ghidra/GhidraProvider.ts
index e032ba2683..6666783592 100644
--- a/src/ghidra/GhidraProvider.ts
+++ b/src/ghidra/GhidraProvider.ts
@@ -3,7 +3,7 @@ import {
   ghidraPinnedLanguage,
   resolveGhidraAnalysisProfile,
 } from "./GhidraAnalysisProfile.js";
-import { ProviderAdapterError } from "../domain/providerAdapterError.js";
+import { ConfigurationError } from "../domain/configurationErrors.js";
 import { resolveGhidraProject } from "./GhidraProjectSnapshot.js";
 import { DeferredAnalysisClient } from "../providers/DeferredAnalysisClient.js";
 import type { ProviderInspectionScope } from "../application/ProviderInspectionScope.js";
@@ -419,14 +419,7 @@ export class GhidraProvider implements AnalysisProviderCandidate {
           isMachOFormat(target.format)
         )
       )
-        return err(
-          new ProviderAdapterError("ghidra", "resolve_analysis_profile", {
-            diagnostics: {
-              reason:
-                "Existing-project mode supports native ELF/PE/Mach-O programs on POSIX without fresh-import loader preparation or pinned language overrides; use fresh import for this target/host.",
-            },
-          }),
-        );
+        return err(existingProjectUnsupported());
       const project = await resolveGhidraProject(
         this.config.ghidraExistingProject,
         target,
@@ -671,6 +664,15 @@ export class GhidraProvider implements AnalysisProviderCandidate {
   }
 }
 
+/** The selected project, not the target or provider, is what this host cannot serve. */
+const existingProjectUnsupported = (): ConfigurationError => {
+  const constraint =
+    "Existing-project mode supports native ELF/PE/Mach-O programs on POSIX without fresh-import loader preparation or pinned language overrides; unset REA_GHIDRA_PROJECT_PATH to use fresh import for this target/host.";
+  return new ConfigurationError(constraint, {
+    settings: [{ setting: "REA_GHIDRA_PROJECT_PATH", constraint }],
+  });
+};
+
 const providerFailureText = (cause: unknown): string =>
   cause instanceof Error ? cause.message : String(cause);
 
diff --git a/tests/boundary/providers/ghidra/ghidraProjectSnapshot.test.ts b/tests/boundary/providers/ghidra/ghidraProjectSnapshot.test.ts
index 972f3f1e8c..d429cbf689 100644
--- a/tests/boundary/providers/ghidra/ghidraProjectSnapshot.test.ts
+++ b/tests/boundary/providers/ghidra/ghidraProjectSnapshot.test.ts
@@ -196,6 +196,21 @@ it.skipIf(process.platform === "win32")(
   },
 );
 
+it("reports a missing project marker as an invalid REA_GHIDRA_PROJECT_PATH selection", async () => {
+  const root = await createTestTempDirectory("rea-ghidra-project-missing-");
+  await expect(
+    resolveGhidraProject(
+      { path: join(root, "missing", "app.gpr") },
+      { path: join(root, "target") },
+      resources,
+    ),
+  ).rejects.toMatchObject({
+    _tag: "ConfigurationError",
+    settings: [{ setting: "REA_GHIDRA_PROJECT_PATH" }],
+    diagnostics: { system_code: "ENOENT" },
+  });
+});
+
 it.skipIf(process.platform === "win32")(
   "follows native parent symlinks and preserves missing marker failures",
   async () => {