Synchronize the #181 living target with settled XMD contracts

[taras]

Story

As a workflow author, I want the living target in PR #181 to describe current XMD contracts and implementation status accurately, so every production slice builds toward one executable workflow rather than obsolete runtime assumptions.

Scope

• Align declaration, return, error, registration, projection, and namespaced-props vocabulary with current main.
• Incorporate the retained Workspace contract merged in PR 📝 Specify retained workflow Workspaces #358.
• Use the current issue map in Implement retained Workflow Workspace restoration #218 for missing lifecycle, storage, Repository/Worktree, Git/forge, Agent, generated-XMD, Worker Shell, continuation, and certification capabilities.
• Model Repository URLs and bases as ordinary root props or expressions; names provide stable component identity, not magic configuration resolution.
• Keep lexical Dir distinct from explicit Agent.AddDir.
• Keep Agents read-only; represent proposed mutations as constrained generated XMD.
• Keep Git push explicit and separate from PullRequest creation.
• Mark unimplemented components and commands as target behavior until their linked production issues land.

Acceptance

• Every shipped claim is supported by current main; every target claim links to an open implementation issue.
• Workflow frontmatter and all already-supported schemas parse and compile through current main.
• The document contains no refs/xmd/runs ledger, single implicit worktree, writable Agent, hidden Git push, or filesystem replay-guard assumption.
• The target does not label an exhausted failed plan as converged.
• The target uses only current architecture.md terminology.
• Dependencies are acyclic: document proof in Prove the shipped adversarial-planning document logic #290 may run against the PR branch before PR Document adversarial implementation workflow WIP #181 merges.
• PR Document adversarial implementation workflow WIP #181 passes review on a fresh head.

Completion

This issue closes when PR #181 merges. Until then, keep it synchronized as child issues ship.