Slice: Stabilize contract obstruction taxonomy for Jim

[flyingrobots]

Slice

Make Echo contract-hosted obstruction posture precise enough for Jim to translate into product language.

Done when:

• unsupported operation/query, admission obstruction, runtime fault, missing retention, stale basis, residual reading, and budget limit are typed;
• broad strings/catch-all runtime errors are not the product API;
• the taxonomy is covered by tests or fixture witnesses.

Goalpost

Part of Goalpost: Jim Evidence Gate for Echo v0.1.0 under milestone v0.1.0 - Jim Evidence Gate.

[coderabbitai]

🔗 Related PRs

#335 - feat(core): add authority policy obstruction vocabulary [merged]
#358 - feat(core): add admission evidence boundaries [merged]
#365 - feat(wesley): emit query observer host helpers [merged]
#371 - feat(core): advance v0.1 contract evidence and retention [merged]

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[flyingrobots]

Refined by #640.

The Jim obstruction taxonomy should support Supported Outcome Settlement outcomes. In particular, stale basis should be representable as witnessed non-application and, when repair metadata exists, repairable obstruction. Broad runtime errors, terminal obstructions, scheduler rejections, and faults should remain distinct.