Define agent harness execution receipt boundary

[mdheller]

Summary

Adds the SourceOS specification boundary and first machine-checkable schema/example/validator set for agent harness execution receipts.

This makes local-first runtime, browser, terminal, model carry, credential, host mutation, download/artifact, and replay proof signals consumable by AgentPlane, Policy Fabric, Memory Mesh, SCOPE-D, and Delivery Excellence without moving implementation or scoreboards into the spec repo.

Scope

• Adds docs/agent-harness-execution-receipts.md.
• Adds schemas/AgentHarnessExecutionReceipts.json.
• Adds examples/agent-harness-execution-receipts.example.json.
• Adds tools/validate_agent_harness_execution_receipts.py.
• Adds focused CI workflow .github/workflows/agent-harness-execution-receipts.yml.
• Defines receipt semantics for LocalAgentRuntimeReceipt, ShellReceiptEvent, BrowserActionReceipt, ModelCarryRouteReceipt, HostMutationBoundaryReceipt, and DownloadArtifactReceipt.
• Defines Delivery Excellence projections for local runtime success, browser/terminal actions, host mutation posture, credential use, offline/local-only compliance, and replay eligibility.
• Defines Policy Fabric, AgentPlane, Memory Mesh, and SCOPE-D integration expectations.

Validation

• Branch diff is 5 commits ahead, 9 behind current main; update/rebase before merge.
• Changed files are limited to docs, schema, example, validator, and focused workflow.
• No runtime behavior changed.

Related

• Add agent harness delivery operating model SocioProphet/delivery-excellence#9
• Add agent harness metric contracts SocioProphet/delivery-excellence-automation#7
• Route agent harness metrics to Delivery Excellence SocioProphet/sociosphere#273
• Define agent harness runtime contract map SocioProphet/agentplane#107
• Define agent harness policy gate model SocioProphet/policy-fabric#60
• Define agent harness memory ledger contract SocioProphet/memory-mesh#23