Cheatcode install deep-integration (#659): local-scope install + cheatcodes.scope + per-agent attachment

[ZaxShen]

Back-created mirror of local trajectory issue 99 (this issue) (its intent_start sync didn't fire). Work SHIPPED in PR #784 (local-scope install param + cheatcodes.scope column v15 + per-candidate attachment routing). Closing immediately — recorded for completeness. Refs #659, #778.

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[ZaxShen]

Shipped via PR #784 (cheatcode install scope + cheatcodes.scope + per-agent attachment). Mirror of local #99.