Release 0.1.9 #1904

Tracks shipping 0.1.9: 0.1.9 → dev, then publish. Close when 0.1.9 is published.

Everything is on 0.1.9 (integration merged by #1903).

• Batch merged into the integration branch: fix(impact): Python transitive reach — two over-reach sources, Optional class-object params #1891, javascript: a test that never loads the change is not selected; a mocha load-time throw selects the whole run #1894, Agent-asserted call edges: list the sites an answer stops at, link them, walk them as [asserted] (#1892) #1895, TypeScript: multi-line test registrars, runner set-up files, Object.assign function objects, overload implementations (stacked on #1882) #1888, TypeScript test selection: leave out tests that never load the change, type tests, package-imported names (stacked on #1888) #1893 (0.1.9: merge the impact / path / test-selection batch (#1891, #1894, #1895, #1888, #1893) #1897), then fix(csharp): reach loop — accessor dispatch, implicit calls, delegate parameters #1896 (C#) and Java reach: narrower initializer hop, platform boundaries, operator overloads #1898 (Java)
• Cross-platform end-to-end of the build as shipped (packed CLI + prebuilt engine per platform): darwin-arm64, darwin-x64, linux-x64, linux-arm64, win32-x64 — every CLI verb, edit/rebuild rounds in all five languages, every MCP tool, axiomcode link, --library auto. Bar: 0.1.8's result (0 CLI failures, MCP all passing on every platform)
• PR 0.1.9 → dev ("Release 0.1.9"), CI green
• Release pipeline run and npm publish of 0.1.9
• Older open issues the release fixes, verified on its own examples and closed

Issues closed by this release so far: #1887, #1889, #1892, #1897, #1899, #1900, #1901, #1902.