[gandazgul]

Converts the image-attachment test module to TypeScript and updates the isolated-runner inventory. Native SessionManager, image-content, model, and fetch types replace broad annotations; named fixture shapes describe the existing settings and discovery registry. Partial SDK fixtures retain localized compatibility assertions.

All fixtures, assertions, cleanup, process-global locks, and nine test cases remain unchanged. This conversion adds no production behavior.

Validation:

• Frozen root/docs installation with Bun 1.4.3; initialized submodules are clean.
• All 11 preliminary CI checks pass, including type checks, lint, language policy, documentation links, and Workspace build.
• All nine existing image-attachment tests pass; case-count delta is zero.
• Emitted runtime JavaScript AST matches the original test file exactly.
• Independent Standards, Spec, and Tests reviews are clear.
• Full GitHub source and Golden CI required before merge.