ci: scope-gate the examples/ag-ui e2e job and make it block merges

[blove]

Second waste lever after #939, found by auditing every job's if: gate.

examples-ag-ui-e2e had no if: at all. It ran on every push and every pull request — a Playwright suite with a 35-minute timeout, executing on docs-only and website-only PRs. On #932 (three files under apps/website/src) it ran to completion for nothing.

It was also absent from required-pr-checks, so an ag-ui e2e failure never blocked a merge. Both halves are fixed here deliberately: gating it without requiring it would leave a suite that is skipped often and ignored when it fails — the worst of both.

The plumbing was half-built, not missing

examples/ag-ui/project.json and examples/ag-ui/angular/project.json already carried scope:examples-ag-ui. But examples_ag_ui was never added to SCOPE_KEYS, so classifyFromAffected read the tag and discarded it (SCOPE_KEYS.includes('examples_ag_ui') → false). There was simply no output for the job to gate on. The removed comment said as much: "No dedicated ci-scope output exists for examples/ag-ui yet."

Not buying speed with coverage

examples/ag-ui/python/project.json had no tags at all. That's the backend the e2e job uv syncs and drives the Angular app against, so scoping the job while leaving the backend untagged would have made a python-only change silently skip the suite. It's tagged here. examples/chat/python already carries its scope:examples-chat tag exactly this way.

Verified against real commits

change	examples_ag_ui
website-only (#932 base..head)	false
an examples/ag-ui/angular change	true
an isolated python-only change	true (with examples_chat and website both false)

Tests

Five specs, all confirmed failing first:

not ok 1 - an affected examples/ag-ui project selects examples_ag_ui only
not ok 2 - the python backend the e2e job uv-syncs owns the scope too
not ok 3 - a website-only change leaves examples_ag_ui false
not ok 1 - contains the 13 documented scope keys
not ok 16 - scope-gates the examples/ag-ui e2e job and requires it

The existing provides one stable required PR check that waits for scoped CI jobs guard also fired on the needs addition — that guard doing its job — and its expected list is updated. 137/137 node --test after; nx lint scripts clean.

🤖 Generated with Claude Code

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