canon(methods): add CF Agents Week substrates (DOs + Agents SDK, Project Think, Dynamic Workflows, Dynamic Workers)

[klappy]

Adds the Cloudflare Agents Week (April 2026) substrates to klappy://canon/methods/spawned-agent-session-substrate-options, plus the execution-ladder composition pattern.

What this PR does

Eight surgical splices to canon/methods/spawned-agent-session-substrate-options.md:

1. Summary — adds a fifth observation on substrate properties beyond price (hibernation, trigger surface, session shape, composition).
2. New substrate section — Cloudflare Durable Objects + Agents SDK + Project Think, with hibernation as the defining property, native trigger-surface diversity (HTTP/WS/alarm/email/RPC/queue/object-store), and two worked examples (subscribed observer at <$0.001/8hr wall-clock; one-shot dispatch at ~$0.0005).
3. New substrate section — Cloudflare Dynamic Workflows, with dispatch-time code injection as the defining property and validator → resolver → re-validator as the worked example.
4. New substrate section — Cloudflare Dynamic Workers, distinguished from Sandboxes by millisecond-boot isolates vs container provisioning.
5. New composition section — Substrate Composition / Execution Ladder (Tier 0 DO → Tier 1 Dynamic Worker → Tier 2 npm → Tier 3 browser → Tier 4 Sandbox), with a substrate-can-dispatch-to-which-other-substrate matrix.
6. Things-That-Do-Not-Vary — adds the canonical session contract bullet pointing at klappy://canon/methods/spawned-agent-session-runtime-contract.
7. When-To-Pick decision tree — adds (4a) subscribed/long-lived session shape → DOs, and (4b) multi-step durable workflow → Dynamic Workflows.
8. Relationship / See Also / Notes on Aging — adds runtime-contract relationship, four new CF blog and docs references, and a dating note for 2026-05-11.

Forward reference

This commit forward-references klappy://canon/methods/trigger-source-taxonomy in the trigger-surface diversity bullet. That doc is drafted (5962 words on the operator's machine) and pending its own PR; the forward reference is intentional so this doc names the dispatch-routing layer where it belongs.

What did NOT change

The substrate-pattern framing — concrete substrates as illustrations of properties, not vendor marketing — is preserved. All existing sections retain their original content. Cost numbers in existing sections were not re-priced; only the new sections carry May 2026 numbers, and the Notes-on-Aging dating note tags the update date for future auditors.

Status

status: draft on the existing doc frontmatter is unchanged. This addition is additive, not a stability promotion.

---

Note

Low Risk
Low risk because this PR only updates a canon markdown method doc; no runtime code paths or configuration are changed.

Overview
Updates spawned-agent-session-substrate-options.md to broaden the substrate catalog beyond Sandboxes/Managed Agents by adding Cloudflare Agents Week primitives: Durable Objects + Agents SDK (and preview Project Think), Dynamic Workflows, and Dynamic Workers, including new billing dimensions, defining properties (hibernation, trigger surface, millisecond-boot isolates), and worked cost-shape examples.

Expands the selection guidance with an execution-ladder composition section (DO → Dynamic Worker → npm → browser → Sandbox) and a dispatch-capability matrix, adds decision-tree branches for subscribed and multi-step durable session shapes, and cross-links the substrate-independent spawned-agent-session-runtime-contract plus new dating/see-also references.

^{Reviewed by Cursor Bugbot for commit e3fac03. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

Canon Quality — Frontmatter Schema ✅

All 40 file(s) in writings/ conform to klappy://canon/meta/frontmatter-schema.

_{Validator: scripts/validate-frontmatter.py · Canon: klappy://canon/constraints/frontmatter-validation-before-merge · Run: #126}

[github-actions]

Canon Quality — oddkit_audit ✅

No dead klappy:// references or legacy link patterns found in writings/. 39 files scanned.

_{Spec: klappy://docs/oddkit/specs/oddkit-audit · Workflow: .github/workflows/canon-quality.yml · Run: #126}