Expose browser pool viewport

[IlyaasK]

Summary

• expose computed nested viewport on kernel_browser_pool
• preserve omitted viewport as a typed null object
• require positive width/height and optional positive refresh rate
• reject explicit null, malformed objects, missing dimensions, and invalid child values
• update generated Registry docs

Scope

Additive v1 durable read state only. Chrome policy and live acceptance remain separate; no runtime/session fields are exposed.

Tests

Ran focused tests repeatedly, race tests, full short suite, vet, gofmt, module checks, Terraform example fmt, docs drift, and diff checks.

Coverage includes Framework nested-state roundtrip, typed-null omission, omitted refresh rate, malformed/null viewport, missing and non-positive dimensions, invalid refresh rate, and wrong JSON types.

Acceptance not run; live viewport payload behavior remains for the opt-in acceptance slice.

Additional quality verification

• Gremlins: 40/40 mutants killed after adding the minimum-positive viewport regression test; targeted semantic mutations: 5/5 killed
• browser-pool data-source coverage: 94.3%; maximum CRAP score: 15.0
• Godog stack suite: 7 scenarios / 21 steps passed, including the @pr78 minimum-viewport scenario

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Note

Low Risk
Additive read-only computed state on an existing data source with validation and broad unit tests; no write paths or auth changes.

Overview
Adds a computed nested viewport attribute to the kernel_browser_pool data source so Terraform can read pool browser window settings from the API.

When the API omits viewport, state uses a typed null object (not unknown). When present, width and height must be positive integers; refresh_rate is optional and must be positive when the field is present. Malformed or invalid API payloads (null viewport, wrong types, missing dimensions, zero/negative values) surface as invalid-response diagnostics instead of silent bad state.

Registry docs for the data source are updated to document the nested schema. Unit tests cover schema semantics, read roundtrip, omission, optional refresh rate, minimum values, and rejection cases.

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[IlyaasK]

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