[react-devtools-shared] Fix URL construction when base URL is invalid (#34407)

### Problem
- Users encounter “Failed to construct 'URL': Invalid base URL” when
clicking the “View source” action in DevTools if the underlying base URL
is invalid.
- This exception originates from `new URL(relative, base)` and bubbles
up, interrupting the DevTools UI.
- Fixes GitHub issue
[#34317](https://github.com/facebook/react/issues/34317)

### Solution
- Wrap URL construction to:
  - First try `new URL(sourceMapAt, sourceURL)`.
  - If that fails, try `new URL(sourceMapAt)` as an absolute URL.
  - If both fail, return `null` (no symbolication) rather than throwing.
- This preserves normal behavior for valid bases and absolute URLs,
while avoiding crashes for invalid bases.

### Implementation details
- Updated `symbolicateSource` in
`packages/react-devtools-shared/src/symbolicateSource.js` to handle
invalid base URL scenarios without throwing.
- Added/verified tests in
`packages/react-devtools-shared/src/__tests__/utils-test.js`:
- “should not throw for invalid base URL with relative source map” →
resolves to `null`.
- “should resolve absolute source map even if base URL is invalid” →
still resolves correctly.

### Test plan
- Lint/format:
  - `yarn prettier-check`
  - `yarn linc`
- Type checking:
  - `yarn flow dom-node`
- Unit tests:
  - `yarn test --watchAll=false utils-test`
  - Optionally: `yarn test --watchAll=false utils-test inspectedElement`
- All of the above pass locally for experimental channel.

### Risks and rollout
- Risk: Low. Only affects cases where the base URL is invalid.
- Normal cases (valid base or absolute `sourceMappingURL`) are
unchanged.
- No user-facing API changes; DevTools UX becomes more resilient.

### Affected packages
- `react-devtools-shared`

### Related
- Fixes GitHub issue
[#34317](https://github.com/facebook/react/issues/34317)

### Checklist
- [x] Ran `yarn prettier-check`
- [x] Ran `yarn linc`
- [x] Ran `yarn flow dom-node`
- [x] Relevant unit tests passing
- [x] Linked issue and added a concise summary


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packages/react-devtools-shared/src/__tests__/utils-test.js

@@ -421,6 +421,26 @@ function f() { }
       await expect(run('http://test/c.mjs')).resolves.toStrictEqual(result);
       await expect(run('http://test/d.mjs')).resolves.toStrictEqual(result);
     });
+
+    it('should not throw for invalid base URL with relative source map', async () => {
+      const fs2 = {
+        'bundle.js': `${source}bundle.js.map`,
+      };
+      const fetch2 = async url => fs2[url] || null;
+      const run = url => symbolicateSource(fetch2, url, 1, 1);
+      await expect(run('bundle.js')).resolves.toBe(null);
+    });
+
+    it('should resolve absolute source map even if base URL is invalid', async () => {
+      const fs3 = {
+        'invalid-base.js': `${source}http://test/a.mjs.map`,
+        'http://test/a.mts': `export function f() {}`,
+        'http://test/a.mjs.map': `{"version":3,"file":"a.mjs","sourceRoot":"","sources":["a.mts"],"names":[],"mappings":";;AAAA,cAAsB;AAAtB,SAAgB,CAAC,KAAI,CAAC"}`,
+      };
+      const fetch3 = async url => fs3[url] || null;
+      const run = url => symbolicateSource(fetch3, url, 4, 10);
+      await expect(run('invalid-base.js')).resolves.toStrictEqual(result);
+    });
   });
 
   describe('formatConsoleArguments', () => {

packages/react-devtools-shared/src/symbolicateSource.js

@@ -75,7 +75,18 @@ export async function symbolicateSource(
         resourceLine.length,
       );
 
-      const sourceMapURL = new URL(sourceMapAt, sourceURL).toString();
+      // Compute the absolute source map URL. If the base URL is invalid, gracefully bail.
+      let sourceMapURL;
+      try {
+        sourceMapURL = new URL(sourceMapAt, sourceURL).toString();
+      } catch (e) {
+        // Fallback: try if sourceMapAt is already an absolute URL; otherwise give up.
+        try {
+          sourceMapURL = new URL(sourceMapAt).toString();
+        } catch (_e) {
+          return null;
+        }
+      }
       const sourceMap = await fetchFileWithCaching(sourceMapURL).catch(
         () => null,
       );