feat(demo): start-chat confirmation page, question after # (founder ruling 2026-10-03)

[trakhimenok]

What

Founder ruling 2026-10-03 (backstage docs/design/demo-as-github-project.md, "Founder ruling 2026-10-03", 3.1, 6.5): the demo hand-off goes to a confirmation page …/start-chat with the question after #. The demo flag stays off; nothing here turns the demo on. Landing deploys to the live app, so please review before landing.

All paths below are under apps/datatug-app/.

Required behaviour, where it is, and the test

#	Behaviour	Code	Tests
1	New addresses …/start-chat#msg=&lang= and …/tree/<ref>[/<dir>]/-/start-chat#…; q is an alias of msg; URLSearchParams semantics	src/app/demo-handoff-path.ts:36-139 (target start-chat, folder support, startChatSegmentsOf); fragment parsing src/app/demo-handoff-capture.ts:92-145, src/index.html:62-80	demo-handoff-path.spec.ts (targets, router agreement), demo-handoff-capture.spec.ts "the start-chat address: the question after #", "capture of the start-chat address"
2	Inline script (ES5) reads msg/q/lang from the fragment and the query, stashes them as today, replaceStates to the same path with the fragment and those query keys removed (other keys kept); old addresses unchanged in effect; reuses #183's // and root-group normalisation	src/index.html:36-100	script specs in demo-handoff-capture.spec.ts ("acts on exactly the paths isHandoffPath accepts" extended to the fragment; "agrees with the TypeScript on every spelling")
3	The page: the existing holding page and strings; question echoed only for the trusted project (isTrustedHandoff), neutral wording otherwise, same two actions; a reload shows the question from the tab's stash; seam for "Start"	src/app/demo-holding-page.component.ts (readView, TODO(G-A4b) at :65), src/app/demo-handoff-asked.ts:183 (handoffDecision: start-chat is always the page), src/app/demo-handoff-capture.ts:60-85 (trust: a folder is never trusted)	demo-holding-page.component.spec.ts "…on the start-chat address", demo-handoff-asked.spec.ts "the decision for an address", datatug-app-routes.spec.ts "start-chat"
4	/chat never reads a question	the chat route is not the page any more; handoffDecision returns none for …/chat without a stashed question, and the page code reads no question from it	datatug-app-routes.spec.ts, e2e "the project chat page never reads a question"
5	Old addresses move to the new page: …/chat?msg= and ?q= are replaced by …/start-chat (no question in the address); /demo?q=…&scenario=…&lang=… stays as today; the router safety net that removes msg/q under /project/github.com/ is untouched	src/app/datatug-app-routes.ts:77-92 (RedirectCommand, replaceUrl: true)	datatug-app-routes.spec.ts (move, replaces history, keeps case of ref), e2e "the old chat address with a question is replaced by start-chat: Back does not return to it", "/demo?q=…&scenario=…&lang=… … still shows the holding page"
6	Privacy, production build, third parties stubbed and recorded	—	e2e/demo-handoff.spec.ts "the start-chat confirmation page": for fragment, fragment with q, query, query with another key, old chat (msg, q), // and root-group spellings, each on the demo project and on acme/demo: address bar, every history entry (Navigation API), history.* calls, title, storage (only the existing per-tab hand-off key, trusted only), own and third-party requests carry no question; the trusted project echoes it, acme/demo is neutral. Plus: a fragment question is in no request at all, not even the document request or a referrer

Choices where the design was silent

• Bare …/start-chat (no fragment) shows the same holding page with nothing to confirm (the no-question sentence for the trusted project, neutral wording otherwise). It does not open the project chat: 6.5 row 2 says the holding page, and the chat of a GitHub project shows a data error until G-A7. Tested.
• "Start" button: none while the flag is off (6.5 has none); a TODO(G-A4b) in the component header says where it goes and that the flag is read where demo-flag.ts is read (the spec forbids importing it here).
• Folder support is for start-chat only. The old …/chat address keeps its shape (no folder), as today. A start-chat address in a folder or on a ref other than HEAD is a hand-off address and is never trusted.
• A fragment pasted over the open page (same-document navigation: no reload, the script does not run) is taken by the page and removed from the address: the page state is now a signal re-read on a hand-off navigation that carries a hand-off key. Found by an e2e case; unit tested.
• The router rewrites //project/… and /(project/…) spellings to the plain address on first navigation; the question is gone either way.
• A #msg= on …/chat or any other page is not a hand-off (no new special cases); it is neither read nor stripped there.
• Stored-for-reload key of an old …/chat?msg= is written by the script under the chat path and rewritten under the start-chat path by the page on first render (a reload in the few milliseconds between shows the page without the question).

Checks

• Unit: vitest app project, 708 tests pass (14 files). pnpm run check:zoneless OK. nx lint datatug-app passes, no findings.
• E2E playwright.demo-handoff.config.ts against the production build: 113 passed (was 82; the 7 old-chat cases that asserted the address stays …/chat now assert …/start-chat). The config's own webServer could not start under wb run in this worktree (the nested pnpm nx serve exits 1 at once), so the production dev-server was started separately and reused.
• Initial bundle, production build, origin/main a248156 vs this branch: main chunk 1,227,478 to 1,228,168 bytes raw (+690 B), 324,975 to 325,189 gzip (+214 B); nx "Initial total" 2.10 MB both, estimated transfer 470.90 kB to 470.94 kB.
• Not touched: in-app link builders, storage, github-project-routes.ts, datatug-routing-*.

Screenshots (390 and 1280; trusted en and ru with a question, bare, untrusted): /private/tmp/claude-501/-Users-alex-projects/27bc30d5-3ff1-4e50-a5d9-9c67e328b1e3/scratchpad/apps-start-chat/shots/.

🤖 Generated with Claude Code

[trakhimenok]

[review r1 #186] Adversarial review (Opus): production builds of this head and of main served side by side; 52 hand-off addresses plus the earlier review's 153; Back/Forward/reload, pasted fragment, 6 KB message, HTML payload; GA stand-in, Navigation API, PostHog and Sentry bodies recorded with positive controls; 3,125 unit tests; mutants of every start-chat branch.

Reviewed-Head: 8a6238e

No question leaks or is echoed where main protected it. /demo behaves exactly as on main, so the live datatug.io button is unaffected. Old …/chat?msg|q= addresses land on the same project's start-chat (history replaced); every other route behaves as on main. The question is echoed only for datatug/chinook-demo at the root (short form or tree/HEAD/-/start-chat), neutral otherwise (Kelvin sign, long s, folder, 40-hex ref, look-alike repos), as text only. The inline script is ES5, first in <head>, same-origin only, stripping nothing outside hand-off paths.

Minors, carried to #184:

1. A pasted fragment is stripped from the address bar through raw history.replaceState (demo-holding-page.component.ts:596, demo-handoff-capture.ts:339), but the router keeps #msg= in its own URL; a later failed navigation can put it back, and Sentry's navigation breadcrumb records it. Main is worse in every part. Strip through Angular (Location.replaceState / router.navigate([], {fragment: undefined, replaceUrl: true, queryParamsHandling: 'preserve'})); add the breadcrumb scrubber planned in G-A4b.
2. A reload in the milliseconds after …/chat?msg= loses the question (src/index.html:692-697 saves under the /chat path); save directly under the start-chat path.
3. datatug-app-routes.spec.ts:273 ("the move replaces the old address in the history") passes with replaceUrl removed; start from a recorded /chat?q= entry and count entries. Browser behaviour is correct.
4. A fragment on a non-hand-off address (…/chat#msg=, /demo#msg=) is left alone, as on main; the sites never build these.

Not verified: PostHog event bodies (only /flags sent under the stubs; the question element keeps ph-no-capture), real GA4 enhanced-measurement page views, browsers other than Chromium.

VERDICT: blockers=0 majors=0 minors=4 land=yes

🤖 Generated with Claude Code