feat: say so when Tangent cannot be reached

[camielvs]

Now that a project tile and a freshly created project both open a Tangent session, a Tangent that isn't running is something you land on rather than something you have to go looking for. Today that shows a blank page, with only an uncaught rejection in the console to say why.

Tangent isn't reachable
Nothing answered at http://localhost:5173, so this project cannot be opened. Check that Tangent is running and that the workspace points at the right address.
[ Try again ]

Why not an error boundary

The failure is an async rejection, not a render error, so a boundary would never catch it. TangentProvider does:

const [readyPromise] = useState(() => loadEmbedRuntime(url));
useEffect(() => { void readyPromise.then(() => setReady(true)); }, [readyPromise]);

There's no .catch. When the import rejects, ready stays false forever and the provider renders <tangent-provider> with null children — hence the blank page.

How this observes it

loadEmbedRuntime isn't exported from @tangent/embed-react, so useTangentRuntime performs the same dynamic import and watches both outcomes. Module imports are cached per URL by the browser, so this does not fetch twice — the provider's own import resolves against this one.

To remove any chance of the probe and the provider disagreeing about what was tried, the URL is built once and passed to the provider via its existing channelUrl prop (which is documented as defaulting to exactly this path).

A failed module import stays failed for the life of the document, so Try again reloads the page rather than retrying in place.

Scope

TangentProjectPage gains two lines and an early return; the view is its own component so it can be tested — nothing under Tangent/ has component tests, only hooks and services.

Testing

pnpm run validate clean; 2984 tests pass, 6 new.

Verified in a real browser against the dev server with tangent-shell on and no Tangent running: the page now shows the box instead of blank, in both light and dark, and the two uncaught TypeError: Failed to fetch dynamically imported module rejections are gone (the early return means the provider never starts its unhandled import). The ERR_CONNECTION_REFUSED network log remains, as it must.

Not verified: the path where Tangent is reachable — it isn't set up locally. That path is unchanged apart from receiving an explicit channelUrl equal to the default it already computed.

🤖 Generated with Claude Code

[github-actions]

🎩 Preview

A preview build has been created at: 09-18-feat_say_when_tangent_is_unreachable/fe2475f

[camielvs]

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• fix(tangent): stop the tab strips scrolling up and down #2777 : 2 dependent PRs (#2779 , #2784 )
• feat(projects): make the agents' instructions a project document #2776
• feat(tangent): list the pipelines the backend holds #2775
• feat(projects): show a project's documents on both pages #2774
• fix(tangent): project window parity — share, new-session links, agent-created pipelines, and a folded-away project window #2773
• refactor(projects): describe a project's resources one way #2765
• feat(projects): delete and share a project from either page #2764
• feat: open a new project ready to work in #2763
• feat: let the project page and Tangent reach each other #2762
• fix: keep a long project name inside the tile it belongs to #2761
• feat: say so when Tangent cannot be reached #2760 👈 (View in Graphite)
• feat: open a project where the work happens #2759
• feat: run a pipeline inside a project #2754
• feat: add pipelines held in this browser to a project #2745
• feat: project page #2738
• feat: create a project from a tile in the grid #2735 : 2 other dependent PRs (#2736 , #2737 )
• feat: projects dashboard #2734
• chore: tangent - annotate runs submission to projectid #2758
• fix: tangent - proper debug sequence system prompt #2757
• fix: tangent - quick run button from mini content window #2744
• fix: tangent - remote agent send delta immediately #2743
• fix: tangent - mint proper authorization with tangent #2742
• feat: tangent - debug in tangent sequence #2741
• chore: add autolayout tool #2740
• feat: tangent - resource management via document entity #2733
• feat: tangent - interactive chips in tangent chat #2732
• chore: save id stack to replay ids on reloads #2731
• refactor: tangent - migrate tangetproectcontext onto mobx #2730
• feat: tangent - keep track of open tabs while switching sessions inside project #2729
• feat: tangent - remote agent for runview and editor #2728
• refactor: tangent - structured workarea target #2727
• feat: tangent - embedded pipeline run view #2726
• feat: tangent - embedded pipeline editor #2725
• feat: tangent - dynamic workarea remote tools #2724
• feat: tangent - resources management in project view #2723
• feat: tangent project view page #2722
• feat: workspaces and projects service #2720
• chore: api client for workspaces and projects #2719
• master

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