docs(scheduler): Investigate pull-based scheduler implementation (#2267)

* docs: scheduler graph investigation - pull-based scheduling & throttling

Detailed analysis of proposed changes:
1. Pull-based scheduling using effect/sink as demand roots
2. Cycle detection and adaptive throttling
3. Automatic debouncing for slow computations

Includes phased implementation plan with risk assessment.

* docs: revise scheduler investigation - phase ordering and cycle semantics

Key updates:
- Swap phases 1 and 2: effect marking must come first
- Clarify that storage handles memoization (no explicit caching needed)
- Add detailed explanation of how cycle semantics change with pull-based:
  - Push: cycles iterate across scheduler batches
  - Pull: cycles iterate within single pull chain
- Convergence strategy: fast cycles complete before effect, slow cycles yield
- Explain phase dependency chain

* docs: detailed scheduler implementation plan

Comprehensive step-by-step implementation guide covering:

Phase 1: Effect Marking
- Add effect/computation distinction to subscribe()
- Mark sink() callbacks as effects
- Build reverse dependency graph
- Diagnostic APIs

Phase 2: Pull-Based Core
- Dirty tracking with transitive propagation
- Feature flag for pull mode
- Modified storage change handler
- pullDependencies() for effect execution

Phase 3: Cycle-Aware Convergence
- Compute time tracking
- Cycle detection via pull stack
- Fast cycle convergence (< 16ms)
- Slow cycle yielding with continuation

Phase 4: Throttling & Debounce
- Debounce infrastructure
- Auto-detection of slow actions
- Declarative debounce API

Includes testing strategy, rollout timeline, and rollback plan.

* docs: move scheduler docs to docs/specs/pull-based-scheduler

* docs: restructure scheduler plan for agent execution

Reformatted implementation plan with:
- Checkbox tasks that agents can tick off as they complete
- Clear prerequisites section
- Phase dependencies explicitly stated
- Grouped tasks by file being modified
- Verification checklist at end of each phase
- Progress summary table for tracking
- Testing commands reference
- Rollback plan per phase

* fix: correct test file path in scheduler implementation plan

Tests are in packages/runner/test/, not packages/runner/src/

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Co-authored-by: Claude <[email protected]>

Author: seefeldb