fix(network): restore model-driven body fetch flow

[lynnswap]

Purpose

• restore network body fetching to a model-driven selected-entry flow
• treat missing network body APIs as an engine readiness contract issue
• keep transient body-agent unavailability recoverable inside the engine instead of the UI

Main changes

• restore selected-entry body fetch orchestration in WINetworkModel, including attach-time follow-up for the current selection
• add NetworkBodyFetchResult plus body-fetch readiness probing, self-heal, and a one-time in-engine retry path in NetworkPageAgent and NetworkSession
• cancel stale selected-entry body fetches when selection changes or the session detaches
• remove UIKit and AppKit body fetch triggers so detail and preview views stay display-only
• update engine, integration, and UI coverage for selected-entry fetch flow, transient agent recovery, and stale-fetch cancellation
• align the AppKit long integration toolbar expectation with the current network toolbar layout

Testing

• mcp__XcodeBuildMCP__test_sim (WebInspectorEngineTests, iPhone 17, latest iOS)
• mcp__XcodeBuildMCP__test_sim (WebInspectorIntegrationTests, iPhone 17, latest iOS)
• mcp__XcodeBuildMCP__test_sim (WebInspectorUITests, iPhone 17, latest iOS)
• mcp__XcodeBuildMCP__test_sim (WebInspectorIntegrationLongTests, targeted AppKit toolbar expectation update; no executable tests on iOS simulator because the case is #if canImport(AppKit))
• codex-review --base origin/codex/dom-graph-store-ssot

Screenshots

• Not included (no intentional visual UI changes)

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Skip handle API repair when reference fallback is available

When a body has both a ref and a handle, performBodyFetch can successfully fall back to getBody(ref, ...) if getBodyForHandle is missing, but this call still declares requiresHandleAPI: hasHandle. In legacy bridge configurations where handle APIs are intentionally absent, that makes ensureBodyFetchAvailability run repair (reinjection + reconfigure) before every fetch even though reference fetch would already work, adding avoidable script churn and latency on normal body loads.

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[chatgpt-codex-connector]

Allow retries after transient body-unavailable results

A bodyUnavailable result is made terminal because fetches mark the body failed and shouldFetch permanently rejects .failed states. Fresh evidence: the JS agent returns null for unauthorized control-token calls in network-agent-core.ts, and bootstrap/configure eval failures are logged-and-continued in the attach path, so attach-time token/bootstrap hiccups can surface as temporary bodyUnavailable; with this gate, those bodies remain stuck failed for the rest of the session because no subsequent selected-entry fetch can retry.

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