fix: harden evidence secret file handoff

backend/src/workspaces/bindings.ts

@@ -60,18 +60,18 @@ function isInside(path: string, root: string): boolean {
   return pathRelative !== "" && !pathRelative.startsWith("..") && !isAbsolute(pathRelative);
 }
 
-function isSafeSecretFile(path: string, secretRoots: readonly string[]): boolean {
-  if (!isAbsolute(path)) return false;
+function safeSecretFilePath(path: string, secretRoots: readonly string[]): string | undefined {
+  if (!isAbsolute(path)) return undefined;
 
   try {
     const resolvedPath = realpathSync(path);
     const resolvedRoots = secretRoots.map((root) => realpathSync(root));
-    if (!resolvedRoots.some((root) => isInside(resolvedPath, root))) return false;
-    if (!statSync(resolvedPath).isFile()) return false;
+    if (!resolvedRoots.some((root) => isInside(resolvedPath, root))) return undefined;
+    if (!statSync(resolvedPath).isFile()) return undefined;
     accessSync(resolvedPath, constants.R_OK);
-    return true;
+    return resolvedPath;
   } catch {
-    return false;
+    return undefined;
   }
 }
 
@@ -132,11 +132,12 @@ export function resolveBinding(
 
     const value = env[variable.name];
     const present = value !== undefined && value.trim() !== "";
-    const safe = !variable.secret || (present && isSafeSecretFile(value, secretRoots));
+    const safePath = variable.secret && present ? safeSecretFilePath(value, secretRoots) : undefined;
+    const safe = !variable.secret || safePath !== undefined;
     if ((required.has(variable.suffix) && !present) || (present && !safe)) {
       missing.push(variable.name);
     }
-    if (present && safe) values[variable.name] = value;
+    if (present && safe) values[variable.name] = variable.secret ? safePath! : value;
   }
 
   return { transport: selectedTransport, values, missing };
@@ -166,11 +167,11 @@ export function resolveEvidenceBinding(
   for (const variable of variables) {
     const value = env[variable.name];
     const present = value !== undefined && value.trim() !== "";
-    const safe = present && isSafeSecretFile(value, secretRoots);
-    if ((required.has(variable.suffix) && !present) || (present && !safe)) {
+    const safePath = present ? safeSecretFilePath(value, secretRoots) : undefined;
+    if ((required.has(variable.suffix) && !present) || (present && safePath === undefined)) {
       missing.push(variable.name);
     }
-    if (safe) values[variable.name] = value;
+    if (safePath !== undefined) values[variable.name] = safePath;
   }
   return { values, missing };
 }

backend/test/workspaces-bindings.test.ts

@@ -1,4 +1,4 @@
-import { chmodSync, mkdirSync, mkdtempSync, rmSync, symlinkSync, writeFileSync } from "node:fs";
+import { chmodSync, mkdirSync, mkdtempSync, realpathSync, rmSync, symlinkSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, expect, test } from "vitest";
@@ -153,7 +153,7 @@ test("resolves direct bindings from the stable workspace namespace", () => {
     values: {
       THT_WS_PSD_CLINICAL_DWH_HOST: "dwh.internal",
       THT_WS_PSD_CLINICAL_DWH_PORT: "5432",
-      THT_WS_PSD_CLINICAL_DWH_PASSWORD_FILE: password.path,
+      THT_WS_PSD_CLINICAL_DWH_PASSWORD_FILE: realpathSync(password.path),
     },
   });
 });
@@ -304,10 +304,26 @@ test("requires only a safe HTTP signed-URL file and never reads its contents", (
     [variable]: signed.path,
     [evidenceVariable("ACCESS_KEY_FILE")]: signed.path,
   }, [signed.root]);
-  expect(resolved).toEqual({ values: { [variable]: signed.path }, missing: [] });
+  expect(resolved).toEqual({ values: { [variable]: realpathSync(signed.path) }, missing: [] });
   expect(JSON.stringify(resolved)).not.toContain("CANARY-SIGNED-URL-CONTENT");
 });
 
+test("canonicalizes an in-root Evidence symlink before passing it to the harness", () => {
+  const signed = secretPath("evidence-signed-target");
+  const link = join(signed.root, "signed-urls-link");
+  symlinkSync(signed.path, link);
+  const source = withEvidence({
+    type: "http",
+    uris: ["https://evidence.example.test/guide.md"],
+    authentication: "signed_urls_file",
+  });
+  const variable = evidenceVariable("SIGNED_URLS_FILE");
+
+  expect(resolveEvidenceBinding(source, { [variable]: link }, [signed.root])).toEqual({
+    values: { [variable]: realpathSync(signed.path) }, missing: [],
+  });
+});
+
 test("requires S3 access and secret files together while accepting an optional safe session token", () => {
   const access = secretPath("evidence-access");
   const secret = secretPath("evidence-secret");
@@ -327,9 +343,9 @@ test("requires S3 access and secret files together while accepting an optional s
   }, [access.root]).missing).toEqual([evidenceVariable("SECRET_KEY_FILE")]);
   expect(resolveEvidenceBinding(source, env, [access.root, secret.root, token.root])).toEqual({
     values: {
-      [evidenceVariable("ACCESS_KEY_FILE")]: access.path,
-      [evidenceVariable("SECRET_KEY_FILE")]: secret.path,
-      [evidenceVariable("SESSION_TOKEN_FILE")]: token.path,
+      [evidenceVariable("ACCESS_KEY_FILE")]: realpathSync(access.path),
+      [evidenceVariable("SECRET_KEY_FILE")]: realpathSync(secret.path),
+      [evidenceVariable("SESSION_TOKEN_FILE")]: realpathSync(token.path),
     },
     missing: [],
   });