feat(framework): P3 — extract Constitution (L0) + gut AGENTS dispatcher (#575)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

packages/mosaic/framework/runtime/claude/RUNTIME.md

@@ -7,7 +7,7 @@ Claude-runtime behavior only. Global rules win if anything here conflicts.
 1. Follow the Session Start load order in `~/.config/mosaic/AGENTS.md`.
 2. Runtime config lives in `~/.claude/settings.json` (hooks, model, plugins, permissions) and
    `~/.claude/hooks-config.json`.
-3. sequential-thinking MCP is required.
+3. Structured reasoning (Constitution) binds to the sequential-thinking MCP on this harness; it is REQUIRED — if unavailable, report the failure and stop planning-intensive execution.
 4. First response MUST declare mode per the global contract.
 5. Git wrappers first for issue/PR/milestone ops; runtime-default confirmation prompts do NOT
    override Mosaic hard gates (push/merge/issue-close without routine confirmation).