semantic: add repo ontology starter pack

[mdheller]

Summary

Adds the first machine-readable repo-topology starter pack for the SourceOS / AgentOS lane.

This PR introduces:

• a shared JSON-LD context for repo descriptors
• a starter role vocabulary / ontology graph
• a JSON Schema for repo descriptors
• a guide for downstream repo adoption
• example descriptors for the current controller / spine / conformance / substrate / commons / public-surface lanes

Why

The README topology work made the role map legible to humans. This PR makes it legible to machines.

The intended next step is for each core repo to publish a semantic/repo.jsonld descriptor that references this shared vocabulary instead of redefining its own ontology.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve existing type mappings in semantic context

Repointing srcos to urn:sourceos:repo-ontology: here effectively replaces the prior https://schemas.srcos.ai/v2/ vocabulary for the same semantic/context.jsonld path, so previously valid JSON-LD documents (for example those using @type: "Dataset" with this shared context) no longer expand to their established IRIs. Because consumers reference this file by URL, changing its semantics in place is a breaking compatibility regression for existing tooling.

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[chatgpt-codex-connector]

Define TopologyRole as an explicit IRI term

Each ontology node uses @type: "TopologyRole", but TopologyRole is not declared in the loaded context and no @vocab is set, so JSON-LD expansion treats this as a relative IRI tied to the document base URL. That makes the class identifier environment-dependent instead of canonical, which undermines cross-repo reasoning over the role class.

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[mdheller]

@copilot fix the failed tests

[Copilot]

@copilot fix the failed tests

Fixed in f0391b1. Two issues were addressed:

1. Validate JSON-LD: repo-ontology.jsonld uses a string @context reference ("./context.jsonld"), which caused 'str' object has no attribute 'items' when the validator tried to iterate it. Added an isinstance(ctx, dict) guard before calling .items().

2. Validate JSON Schemas: ajv-cli@5 defaults to draft-07 and couldn't load the https://json-schema.org/draft/2020-12/schema meta-schema used by all schemas in the repo. Fixed by adding --spec=draft2020 to the ajv compile command. Also fixed cross-schema $ref resolution (e.g. AgentSession.json → ExecutionSurface.json) by passing all sibling schemas as -r references when compiling each schema — all 54 schemas now compile cleanly.