Add traverse-starter.validate and traverse-starter.summarize WASM agents for pipeline showcase

[enricopiovesan]

Summary

Add two WASM agents for the traverse-starter multi-capability pipeline (reference-apps #110):

Capability	Input	Output
traverse-starter.validate	{ note }	{ valid: bool, issues: string[] }
traverse-starter.summarize	process output fields	{ summary: string, wordCount: number }

traverse-starter.process already exists (#499).

Why

Single-capability execute hides workflow composition. Pipeline showcase needs validate + summarize steps.

Depends on

• traverse-starter.process agent (exists)
• Multi-capability workflow ticket Multi-capability workflow orchestration: pipeline execute surface for reference apps #558 (pipeline wiring)

Blocked by

• None — can implement against dev sidecar immediately

Definition of Done

• Contract at contracts/examples/traverse-starter/capabilities/validate/contract.json
• Contract at contracts/examples/traverse-starter/capabilities/summarize/contract.json
• WASM agent examples/traverse-starter/validate-agent/ (Rust + .wasm)
• WASM agent examples/traverse-starter/summarize-agent/ (Rust + .wasm)
• Both agents deterministic: no network, no model, no randomness
• Component manifests with wasm digests
• traverse-starter.validate: empty note → valid: false, issues non-empty; valid note → valid: true, issues: []
• traverse-starter.summarize: produces summary string + word count from process output
• Determinism tests for both agents

Validation

# validate
curl -sf -X POST http://127.0.0.1:8787/v1/workspaces/local-default/execute \
  -H 'Content-Type: application/json' \
  -d '{"capability_id":"traverse-starter.validate","input":{"note":""}}'

# summarize (after process output available in pipeline context)
# Integration via traverse-starter.pipeline (#558)

Downstream unblocked

• reference-apps #110 — traverse-starter pipeline