fix review finding: an export list surfaces only the declarators it names

A name resolved through an export list (or a default-export identifier)
mapped back to its whole VariableStatement, and checkDecl walked every
declarator — so a private sibling sharing the statement with an exported
const was wrongly required to carry JSDoc.

The scope dispatch is now two-phase: requests accumulate per statement
(null = whole statement for a direct export modifier or ambient scope;
name sets union across lists, so two lists naming different declarators
of one statement both count), then each surfaced statement is checked
once with the declarator filter. Regressions pin the private-sibling
skip, the cross-list union, and the default-export sibling.

packages/core/agent/tests/verify-export-jsdoc.spec.ts

@@ -160,6 +160,36 @@ describe('verify-export-jsdoc export forms', () => {
     ))).toEqual([expect.stringMatching(/exported function 'f' .* has no JSDoc\./)])
   })
 
+  it('does not treat a never-exported sibling declarator as surface (review round 2)', () => {
+    // `export { publicValue }` resolves to the whole variable statement; only
+    // the named declarator is surface — the gate must not demand JSDoc for
+    // the private sibling sharing the statement.
+    expect(collectExportJsdocViolations(make(
+      '/** The public knob. */\nconst publicValue = 1, privateHelper = 2\nexport { publicValue }\nvoid privateHelper\n',
+    ))).toEqual([])
+  })
+
+  it('unions declarators across multiple export lists over one statement (review round 2)', () => {
+    // Two lists each name one declarator of the same undocumented statement:
+    // both are surface (deduplicating on first resolution would drop `b`),
+    // while the never-exported `c` stays out.
+    const violations = collectExportJsdocViolations(make(
+      'const a = 1, b = 2, c = 3\nexport { a }\nexport { b }\nvoid c\n',
+    ))
+    expect(violations).toEqual([
+      expect.stringMatching(/exported const 'a' .* has no JSDoc\./),
+      expect.stringMatching(/exported const 'b' .* has no JSDoc\./),
+    ])
+  })
+
+  it('scopes a default-export identifier to its own declarator (review round 2)', () => {
+    // `export default` of an identifier reaches the statement through the
+    // same name lookup as an export list; the sibling stays private.
+    expect(collectExportJsdocViolations(make(
+      '/** The app entry. */\nconst app = 1, scratch = 2\nexport default app\nvoid scratch\n',
+    ))).toEqual([])
+  })
+
   it('reports a re-exported module once, at its defining file', () => {
     const violations = collectExportJsdocViolations(fixture({
       'index.ts': "export * from './other.ts'\n",