Summary

• add USELESSKEY-SPEC-0015 to define the real user workflow contract
• define Rust developer, CI/platform, and materialization paths with copyable snippets, positive/negative cases, proof commands, receipt paths, and boundaries
• update the real-workflow lane plan and active goal so the negative fixture taxonomy is the next ready item

User path

A downstream user should be able to start from a job: write Rust tests, run CI/platform bundle workflows, or explicitly materialize fixtures under an output directory.

Boundary

This is a docs/spec slice only. It does not prepare v0.10.0, bump versions, publish, add contract packs, claim provider compatibility, claim production security, or move repo-local proof into the installed CLI.

Proof

• cargo xtask spec-check --strict
• cargo xtask docs-sync --check
• cargo xtask typos
• git diff --check

Receipts

• docs/specs/USELESSKEY-SPEC-0015-real-user-workflows.md
• active-goal status now marks the real-user-workflow spec done and the negative-fixture taxonomy ready

Risk

No fixture generation, deterministic identity, bundle schema, or public API behavior changes.

Rollback

This PR is revertable without invalidating later receipts because it only adds the workflow contract and updates lane metadata.