What Problem This Solves

Production-mode Knip still tracked 20 agent exports that were module-local types, duplicate facade reexports, or test-only type seams.

Why This Change Was Made

• keep nine implementation types module-private
• remove duplicate facade exports while retaining canonical command, model-selection, prompt-state, runtime-context, and harness artifact owners
• derive test-only helper types through Extract and Parameters
• retarget runtime-context marker tests to the canonical module
• leave the transitive ToolSearchCatalogSession surface unchanged

User Impact

None. Runtime behavior, CLI behavior, plugin SDK contracts, and configuration remain unchanged. The internal TypeScript surface and shrink-only dead-export baseline become smaller.

Evidence

• baseline: 1,211 to 1,191, exactly 20 deletions and no additions
• anchored src/agents count: 279 to 259
• production source: +16/-25; tests: +25/-11; baseline metadata: +0/-20
• Testbox tbx_01kxeyye2sknfxc1tkp9ghxjb9: 17 focused files, 539/539 tests passed
• exact production Knip regeneration and enforced deadcode check passed at 1,191
• targeted format, scoped lint, plugin SDK surface check, core types, and core test types passed
• fresh whole-diff autoreview clean, 0.98
• repository-wide audit found no dynamic/string consumers; canonical plugin SDK and runtime artifact types remain exported from their owner modules

Hosted CI was not awaited per maintainer instruction. Newer main commits are disjoint from the touched paths and baseline.