diff --git a/src/application/JavaScriptReturnShapeProjection.test.ts b/src/application/JavaScriptReturnShapeProjection.test.ts
new file mode 100644
index 000000000..91a168025
--- /dev/null
+++ b/src/application/JavaScriptReturnShapeProjection.test.ts
@@ -0,0 +1,166 @@
+import { describe, expect, it } from "vitest";
+
+import { analyzeJavaScriptSemantics } from "../domain/javascriptSemanticAnalysis.js";
+import { completeApplicationCoverage } from "../domain/javascriptApplicationEvidenceSchemas.js";
+import { projectJavaScriptExportReturnShapes } from "./JavaScriptReturnShapeProjection.js";
+
+const projectReturns = (body: string) => {
+  const ir = analyzeJavaScriptSemantics(`export function result() { ${body} }`);
+  const link = ir.moduleLinks.find(
+    ({ exportedName }) => exportedName === "result",
+  );
+  if (link === undefined) throw new Error("Expected the result export");
+  const projected = projectJavaScriptExportReturnShapes({
+    ir,
+    link,
+    modulePath: "fixture.js",
+    baseCoverage: completeApplicationCoverage(),
+  });
+  if (projected === null) throw new Error("Expected exported return shapes");
+  return projected;
+};
+
+const unknownBranchField = {
+  path: "",
+  state: "unknown",
+  value: null,
+  reason: "Branches have incompatible values.",
+};
+
+describe("exported primitive union return shapes", () => {
+  const conditionalCases = [
+    "missing",
+    "unsupported()",
+    '({ key: "value" })',
+    '["value"]',
+    '+"invalid"',
+  ].flatMap((other) => [
+    `condition ? (choice ? "one" : "two") : ${other}`,
+    `condition ? ${other} : (choice ? "one" : "two")`,
+  ]);
+  const logicalCases = [
+    { operator: "||", known: '(choice ? "" : "one")' },
+    { operator: "&&", known: '(choice ? 0 : "one")' },
+    { operator: "??", known: '(choice ? null : "one")' },
+  ].flatMap(({ operator, known }) => [
+    `${known} ${operator} missing`,
+    `missing ${operator} ${known}`,
+  ]);
+
+  it.each([...conditionalCases, ...logicalCases])(
+    "projects an unknown field instead of a definite union for %s",
+    (expression) => {
+      const projected = projectReturns(`return ${expression};`);
+
+      expect(projected.properties.static_return_shapes).toEqual([
+        {
+          source_range: expect.any(Object),
+          value_status: "ambiguous",
+          fields: [unknownBranchField],
+          property_coverage: [],
+        },
+      ]);
+      // Complete return-site collection does not make its values known.
+      expect(projected.properties.return_shape_coverage).toEqual({
+        status: "complete",
+        retained_return_sites: 1,
+        omitted_return_sites: 0,
+        omitted_fields: 0,
+        omitted_property_coverage: 0,
+        projection_complete: true,
+      });
+      expect(projected.coverage).toEqual(completeApplicationCoverage());
+      expect(projected.limitations).toContain(
+        "Return shapes are inferred from inert syntax and do not prove runtime behavior.",
+      );
+    },
+  );
+
+  it("keeps an incompatible object field unknown beside a known literal", () => {
+    const projected = projectReturns(`
+      return {
+        kind: "result",
+        value: condition ? (choice ? "one" : "two") : missing,
+      };
+    `);
+    expect(projected.properties.static_return_shapes).toEqual([
+      {
+        source_range: expect.any(Object),
+        value_status: "object",
+        fields: [
+          { path: "/kind", state: "literal", value: "result", reason: null },
+          { ...unknownBranchField, path: "/value" },
+        ],
+        property_coverage: [{ path: "", status: "complete", omitted: 0 }],
+      },
+    ]);
+  });
+
+  it("retains valid nested unions, duplicates, and null alternatives", () => {
+    const projected = projectReturns(`
+      return condition
+        ? (choice ? "two" : "one")
+        : (other ? "one" : null);
+    `);
+    expect(projected.properties.static_return_shapes).toEqual([
+      {
+        source_range: expect.any(Object),
+        value_status: "union",
+        fields: [
+          {
+            path: "",
+            state: "union",
+            value: [null, "one", "two"],
+            reason: null,
+          },
+        ],
+        property_coverage: [],
+      },
+    ]);
+  });
+
+  it("preserves three independent direct returns without merging their values", () => {
+    const projected = projectReturns(`
+      if (condition) return choice ? "one" : "two";
+      if (other) return missing;
+      return { kind: "object" };
+    `);
+    expect(projected.properties.static_return_shapes).toEqual([
+      {
+        source_range: expect.any(Object),
+        value_status: "union",
+        fields: [
+          { path: "", state: "union", value: ["one", "two"], reason: null },
+        ],
+        property_coverage: [],
+      },
+      {
+        source_range: expect.any(Object),
+        value_status: "unknown",
+        fields: [
+          {
+            path: "",
+            state: "unknown",
+            value: null,
+            reason: "Unbound identifier missing.",
+          },
+        ],
+        property_coverage: [],
+      },
+      {
+        source_range: expect.any(Object),
+        value_status: "object",
+        fields: [
+          { path: "/kind", state: "literal", value: "object", reason: null },
+        ],
+        property_coverage: [{ path: "", status: "complete", omitted: 0 }],
+      },
+    ]);
+    expect(projected.properties.return_shape_coverage).toMatchObject({
+      status: "complete",
+      retained_return_sites: 3,
+      omitted_return_sites: 0,
+      projection_complete: true,
+    });
+  });
+});
diff --git a/src/domain/javascriptSemanticAnalysis.unions.test.ts b/src/domain/javascriptSemanticAnalysis.unions.test.ts
new file mode 100644
index 000000000..25e02aefa
--- /dev/null
+++ b/src/domain/javascriptSemanticAnalysis.unions.test.ts
@@ -0,0 +1,156 @@
+import { describe, expect, it } from "vitest";
+
+import { analyzeJavaScriptSemantics } from "./javascriptSemanticAnalysis.js";
+import { topLevelBinding } from "./javascriptSemanticAnalysis.fixture.js";
+
+const conditionalCandidates = [
+  '"one"',
+  '(choice ? "one" : "two")',
+  '(choice ? "one" : other ? "two" : "three")',
+];
+const incompatibleValue = {
+  status: "ambiguous",
+  reason: "Branches have incompatible values.",
+};
+
+const valueOf = (expression: string) =>
+  topLevelBinding(
+    analyzeJavaScriptSemantics(`const answer = ${expression};`),
+    "answer",
+  ).value;
+
+describe("conditional primitive unions", () => {
+  const cases = conditionalCandidates.flatMap((known) =>
+    [
+      "missing",
+      "unsupported()",
+      '({ key: "value" })',
+      '["value"]',
+      '+"invalid"',
+      "1e309",
+      "1e308 + 1e308",
+    ].flatMap((other) => [
+      `condition ? ${known} : ${other}`,
+      `condition ? ${other} : ${known}`,
+    ]),
+  );
+
+  it.each(cases)("preserves incompatible alternatives in %s", (expression) => {
+    expect(valueOf(expression)).toEqual(incompatibleValue);
+  });
+
+  it.each([
+    [
+      'condition ? (choice ? "two" : "one") : "three"',
+      { status: "union", values: ["one", "three", "two"] },
+    ],
+    [
+      'condition ? "three" : (choice ? "two" : "one")',
+      { status: "union", values: ["one", "three", "two"] },
+    ],
+    [
+      'condition ? (choice ? "two" : "one") : (other ? "one" : "three")',
+      { status: "union", values: ["one", "three", "two"] },
+    ],
+    [
+      'condition ? (choice ? "two" : "one") : (other ? "one" : "two")',
+      { status: "union", values: ["one", "two"] },
+    ],
+    [
+      'condition ? (choice ? "one" : "one") : "one"',
+      { status: "literal", value: "one" },
+    ],
+    [
+      'condition ? (choice ? "one" : "two") : null',
+      { status: "union", values: [null, "one", "two"] },
+    ],
+    [
+      'condition ? null : (choice ? "one" : "two")',
+      { status: "union", values: [null, "one", "two"] },
+    ],
+    ["condition ? null : null", { status: "literal", value: null }],
+  ])("retains exact primitive candidates in %s", (expression, expected) => {
+    expect(valueOf(expression)).toEqual(expected);
+  });
+
+  it("propagates an incompatible nested branch through an outer union", () => {
+    expect(
+      valueOf(
+        'condition ? (choice ? "one" : "two") : (other ? "three" : missing)',
+      ),
+    ).toEqual(incompatibleValue);
+  });
+});
+
+describe("logical primitive unions", () => {
+  // Each left-hand set can select the unresolved right-hand operand at runtime.
+  const operators = [
+    {
+      operator: "||",
+      alternatives: [
+        '""',
+        '(choice ? "" : "one")',
+        '(choice ? "" : other ? "one" : "two")',
+      ],
+    },
+    {
+      operator: "&&",
+      alternatives: [
+        '"one"',
+        '(choice ? 0 : "one")',
+        '(choice ? 0 : other ? "one" : "two")',
+      ],
+    },
+    {
+      operator: "??",
+      alternatives: [
+        "null",
+        '(choice ? null : "one")',
+        '(choice ? null : other ? "one" : "two")',
+      ],
+    },
+  ];
+  const cases = operators.flatMap(({ operator, alternatives }) =>
+    alternatives.flatMap((known) =>
+      ["missing", "unsupported()"].flatMap((other) => [
+        `${known} ${operator} ${other}`,
+        `${other} ${operator} ${known}`,
+      ]),
+    ),
+  );
+
+  it.each(cases)("preserves unresolved alternatives in %s", (expression) => {
+    expect(valueOf(expression)).toEqual(incompatibleValue);
+  });
+
+  it.each([
+    [
+      '(choice ? "" : "one") || "two"',
+      { status: "union", values: ["", "one", "two"] },
+    ],
+    [
+      '(choice ? 0 : "one") && "two"',
+      { status: "union", values: [0, "one", "two"] },
+    ],
+    [
+      '(choice ? null : "one") ?? "two"',
+      { status: "union", values: [null, "one", "two"] },
+    ],
+    ['"one" || "one"', { status: "literal", value: "one" }],
+    ["null ?? null", { status: "literal", value: null }],
+  ])(
+    "retains the conservative primitive union in %s",
+    (expression, expected) => {
+      expect(valueOf(expression)).toEqual(expected);
+    },
+  );
+
+  it.each([
+    'true ? "one" : missing',
+    '"one" || missing',
+    "false && missing",
+    '"one" ?? missing',
+  ])("does not introduce short-circuit evaluation for %s", (expression) => {
+    expect(valueOf(expression)).toEqual(incompatibleValue);
+  });
+});
diff --git a/src/domain/javascriptSemanticValues.ts b/src/domain/javascriptSemanticValues.ts
index 9e7247016..8b56d6ceb 100644
--- a/src/domain/javascriptSemanticValues.ts
+++ b/src/domain/javascriptSemanticValues.ts
@@ -481,10 +481,9 @@ const mergeValues = (
   const primitives = values.flatMap(
     (value) => primitiveCandidates(value) ?? [],
   );
-  return primitives.length === values.length ||
-    values.every(
-      (value) => value.status === "union" || value.status === "literal",
-    )
+  return values.every(
+    (value) => value.status === "union" || value.status === "literal",
+  )
     ? primitiveSet(primitives)
     : { status: "ambiguous", reason: "Branches have incompatible values." };
 };