fix(harbor): validate schema_version in adapt and stamp it in export

[ayushnangia]

Summary

The Harbor interop's own fidelity promise has a hole in it: export() writes a top-level version = "1.0" into the generated task.toml, but the adapter parses a field named schema_version — so the stamped version is invisible to validation, and a task declaring any unknown schema_version adapts silently with whatever semantics this build happens to implement. A task authored against a future or foreign schema should fail adaptation loudly (the same contract as the other invalid-task paths), not adapt wrong.

Changes

• hud/integrations/harbor/adapt.py: new HARBOR_SCHEMA_VERSION = "1.0"; adapt() raises ValueError ("declares unsupported Harbor schema ...") when a task's schema_version is present and differs. Absent stays accepted (unversioned tasks are the historical export shape).
• hud/integrations/harbor/export.py: generated task.toml now stamps schema_version = "1.0" alongside the existing version key, so round-tripped tasks validate against the exact contract they were written by.

Validation

• New tests in hud/integrations/harbor/tests/test_contract.py: unknown schema fails loudly · supported schema adapts · absent schema still adapts.
• pytest hud/integrations/harbor/tests → 65 passed, 0 failed; full suite (hud/tests + capabilities + patches) → 136 passed.

Scope note

Public surface untouched (__all__ stays ["adapt", "export"] per the contract test). This is the schema half of version pinning; if maintainers want task-side pinning (task.toml requiring a HUD version range), that's a follow-up feature and I have the spec sketched.

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Note

Low Risk
Localized Harbor integration validation and export metadata; backward compatible for tasks without schema_version.

Overview
Closes a Harbor interop gap where export() only wrote version = "1.0" while adapt() reads schema_version, so exported tasks were unversioned for adaptation and foreign schemas could adapt silently.

adapt() now enforces HARBOR_SCHEMA_VERSION ("1.0"): if task.toml sets a different schema_version, adaptation raises ValueError with an explicit unsupported-schema message. Missing schema_version still adapts for legacy/unversioned tasks.

export() stamps schema_version = "1.0" in generated task.toml (alongside version) so HUD-exported Harbor folders round-trip under the same contract.

Contract tests cover unknown schema (fail), supported schema (adapt), and absent schema (still adapt).

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