refactor(dev): remove the unreported MCP protocolEra field

[ScriptedAlchemy]

Summary

Remove the protocolEra field from runtime MCP connection state. The MCP client (@modelcontextprotocol/client 2.0.0) has no getProtocolEra method, so client.getProtocolEra?.() always produced undefined and the 'legacy' branch was unreachable. Only test fixtures and the rsc-agent-runtime example stamped 'modern'.

That dead field also hid a real gate failure. McpAppRuntimePreviewService refused any stable session whose protocolEra was undefined, so a session opened through the real client could never satisfy it. The gate now checks the fields a client actually negotiates: capabilities, protocol version, and server identity.

Removal matrix

Removed	Callers migrated	Deleted surface
DevRuntimeMcpConnectionState.protocolEra (agent-bundle/api)	dev registry, runtime MCP routes, rsc-agent-runtime example session	public field
McpClient.getProtocolEra, McpSessionConnectionState.protocolEra	MCP session connect	internal optional method and field
Workbench protocolEra validators	route client, App client, session controller	runtimeEra and three 'legacy' | 'modern' checks

Fixtures in 17 test files drop the field. Strict key checks in the Workbench route and App clients now reject a connection that still carries it.

Verification

On this branch merged with origin/main (f1db114528):

• pnpm build: pass
• pnpm typecheck: pass
• pnpm lint: pass
• pnpm test:unit: pass (311 files, 4,494 tests)
• pnpm test:integration:run: pass (104 files, 1,187 tests; whole pool because a public type changed)
• pnpm docs:site:build: pass (0 broken links across 30,549 anchors, language parity OK)

Part of the legacy-API removal sweep. Does not overlap #810's files.

[changeset-bot]

🦋 Changeset detected

Latest commit: 831ac0e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
agent-bundle	Minor
create-agent-bundle	Patch

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[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-25T00:26:34.504844Z	cd9715c	PR opened

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[pkg-pr-new]

npm i https://pkg.pr.new/ScriptedAlchemy/agent-bundle@836

npm i https://pkg.pr.new/ScriptedAlchemy/agent-bundle/create-agent-bundle@836

npm i https://pkg.pr.new/ScriptedAlchemy/agent-bundle/rsc-markdown-stream@836

npm i https://pkg.pr.new/ScriptedAlchemy/agent-bundle/@agent-bundle/runtime@836

commit: 831ac0e

[ScriptedAlchemy]

Closing. The premise was wrong. @modelcontextprotocol/client 2.0.0 implements Client.getProtocolEra() (dist/index.mjs:3418), deriving 'modern' | 'legacy' from the negotiated protocol version, and the SDK itself branches on it. The earlier search missed it because ripgrep skipped the gitignored dist directory. protocolEra is current MCP protocol metadata, not an agent-bundle compatibility path, so it stays.