Add zapier-workflows skill, consolidated from agent-skills

[BenMcGit]

Summary

Replaces the fragmented durable-workflow skill guidance with a single zapier-workflows skill, following agentskills.io's scoping guidance.

Today, durable workflow guidance lives in two places that duplicate and drift from each other:

• zapier-sdk's own references/workflows.md
• six separate skills in zapier/agent-skills (workflows-install, -doctor, -create, -list, -history, -modify), each repeating the same "Compatibility Gate" boilerplate

Per agentskills.io: "a skill for querying a database and formatting results may be one coherent unit... skills scoped too narrowly force multiple skills to load for a single task, risking overhead and conflicting instructions." Building, testing, deploying, listing, and modifying a workflow is one coherent task a user does in a single sitting — not six.

What changed

• New: skills/zapier-workflows/ — one skill, SKILL.md (77 lines, well under the 500-line/~5k-token budget) that routes to four reference files loaded on demand:
  • references/setup.md — install/auth/EA-access flow (from workflows-install)
  • references/build-and-deploy.md — the 7-phase build/test/deploy flow (from workflows-create, folding in the parts of workflows.md that weren't duplicated: idempotency-key table, naming convention, catch-hook triggers, escape hatches, explorer-subagent pointer)
  • references/list-and-history.md — merged from workflows-list + workflows-history
  • references/modify.md — from workflows-modify
• Removed: skills/zapier-sdk/references/workflows.md and the durable-workflow skeleton in examples.md — both replaced with a pointer to the new skill
• Updated: README.md, AGENTS.md, llms.txt, skills.sh.json, .codex-plugin/plugin.json to register the new skill

Deliberate design choice: dropped the workflows-doctor mechanism

workflows-doctor did two things: (1) a throttled daily freshness check that re-pulled skill content across 6 independently-drifting files, and (2) a hand-maintained sdk_cli_min/sdk_cli_validated compatibility contract between the skill and the SDK CLI. Both existed because the CLI and the skill lived in separate repos with separate release cadences. Now that this is one skill in the same repo as the CLI it documents, I replaced both with zapier-sdk's existing lighter pattern: tell the agent to trust the live zapier-sdk --experimental <cmd> --help output over hardcoded assumptions, rather than maintaining a version-drift detector. Flagging this explicitly in case there's a reason to keep the heavier mechanism I'm not seeing.

Not in this PR

• Evals: #team-agent-discovery raised this consolidation with the team; Chris McLachlan-Lee's cosub-bench eval harness currently points at the agent-skills layout for the install/create/modify skills. That harness needs to be repointed at this new location before/alongside merging — flagging so it isn't dropped.
• Deprecating the 6 skills in zapier/agent-skills: left as a follow-up PR in that repo once this lands, rather than bundling a cross-repo change here.
• MCP: explicitly out of scope for this pass.

Test plan

• zapier-sdk --experimental --help command surface spot-checked against what's documented in build-and-deploy.md / setup.md / modify.md (content carried over verbatim from the source skills, not re-verified against a live CLI in this pass)
• Confirm skills.sh.json schema still validates
• Chris confirms cosub-bench can be repointed at sdk/skills/zapier-workflows