Add comprehensive test coverage for recursive runtime-import graphs

[Copilot]

The runtime-imports macro supports recursive file imports but lacked systematic test coverage for arbitrary dependency graphs. This adds 69 test cases validating complex import patterns.

Test Coverage Added

Graph Topologies (23 tests)

• Trees: balanced binary, wide fan-out (1→10), deep chains (15 levels), unbalanced
• DAGs: diamond patterns, convergent graphs, multi-level dependencies
• Stars: hub-and-spoke, reverse convergence
• Complex: grids, pyramids, layered architectures

Edge Cases & Performance (10 tests)

• Circular dependency detection in complex graphs (length 1-10 cycles)
• Import caching efficiency (validates 19 cache hits on 20 imports)
• Large graphs (50+ files, 5 levels × 4 branches)
• Line range imports with independent caching
• Mixed optional/required imports

Example Test Pattern

// Diamond dependency with caching validation
it("should handle diamond dependency pattern", async () => {
  // Root → [A, B], A → Shared, B → Shared
  fs.writeFileSync(path.join(githubDir, "shared.md"), "Shared content");
  fs.writeFileSync(path.join(githubDir, "path-a.md"), "Path A\n{{#runtime-import shared.md}}");
  fs.writeFileSync(path.join(githubDir, "path-b.md"), "Path B\n{{#runtime-import shared.md}}");
  
  const result = await processRuntimeImports("{{#runtime-import root.md}}", tempDir);
  
  expect(result).toBe("Root\nPath A\nShared content\n---\nPath B\nShared content");
  expect(core.info).toHaveBeenCalledWith("Reusing cached content for shared.md");
});

All 142 tests in runtime_import.test.cjs pass in <100ms.

Original prompt

Add extensive test suite for agentic workflow with runtime-imports macro that recursively import each other. Generate arbitrary graphs of imported files.

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