feat(viewer): interactive solution visualizations via per-task visualize.py

[aktasbatuhan]

Viewer roadmap item E. Adds a "see the solution" view — an interactive picture of what a run's best program actually produced, modeled on AlphaEvolve's solution panel.

The design (as agreed)

A task ships an optional visualize.py beside its evaluator.py — the visualizer is a per-task input, exactly parallel to the evaluator. It exposes one function:

def render(program_path: str) -> str:   # self-contained HTML/SVG fragment (vanilla JS allowed)

Execution: lazy at view-time + cached. Since solutions aren't stored (only code + metrics), the viewer re-runs the best program through visualize.py in a sandboxed subprocess with a timeout (it execs evolved code; the viewer binds to localhost only), and caches the fragment to best/solution_viz.html (invalidated when the program is rewritten). First render ~2–5s, cached ~0.04s. Works retroactively on all existing runs — it only needs the stored best_program.py.

Discovery: by task-dir name under --tasks roots (default examples/), or a visualize.py dropped directly in the bench task dir.

Two reference visualizers (interactive, vanilla JS + inline SVG, no deps, CSS scoped under .kv-sol)

• circle packing — the packing in the unit square; hover a circle for radius/center/share, scroll-to-zoom, drag-to-pan, shading by radius so load-bearing circles read at a glance.
• autocorrelation — the step function f plus its autoconvolution f∗f with the score-driving peak marked in red; hover to read any step's height.

Also

• /setup/{label}/run/{idx}/solution route (graceful "no visualizer" message when absent).
• Dashboard "see the solution" button, shown only when a visualizer is found.
• --tasks CLI flag on kai viewer.
• skills/visualization/SKILL.md documenting the contract for new tasks.

Verification

• test_solution.py (9): visualizer discovery (direct / by-name / none), render+cache cycle (incl. cache invalidation, force, error-reported-not-raised, missing program), and both reference visualizers render hermetically off the committed initial_program.pys.
• test_viewer.py (+2): solution route present/absent paths and the conditional dashboard button.
• Full suite green (333 tests). Verified live in the viewer on real circle + autocorrelation runs.

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