Fix the desktop blank window: Better Auth rejects tauri:// as a base URL [skip-ui-docs]

[RichardHightower]

The big picture

ForgeNotes ships as two products from one React SPA: a web app on Vercel and a macOS
desktop app in a Tauri 2 shell. The web half has been exercised continuously. The desktop
half had never actually rendered — every launch since the desktop path was first wired
showed either a static placeholder or an error boundary.

This PR is the last step of getting the desktop shell to boot:

Step 1: SPA-mode build so a static index.html exists at all   (earlier commits)
Step 2: honest build verification — fail on a scriptless shell (earlier commits)
Step 3: fix the icon filename that broke `cargo tauri build`   (earlier commit)
Step 4: make the desktop window actually render                <== THIS PR
Step 5: sign / notarise the .dmg so it opens off this machine   (not started)

Terms used below. Asset protocol — Tauri serves a packaged app's files from the
custom scheme tauri://localhost rather than over HTTP. Error boundary — a React
component that catches an exception thrown by its children and renders a fallback instead
of crashing; TanStack Router installs one by default. Embed — Tauri copies the frontend
bundle into the compiled binary, so the binary and the bundle on disk can disagree.

The problem this PR solves

The packaged desktop app opened to this, on a blank page:

Something went wrong!   [Show Error]

Four concrete problems sat behind that:

1. The app threw before it rendered anything, and the message was hidden behind a
   button nobody had pressed.
2. The instrumentation added to read that message could not see it. A window.onerror
   listener only fires for uncaught exceptions. A React error boundary catches the
   exception — by design, it never reaches the window. So the reporter logged nothing, and
   that nothing was read as "no error", which is precisely backwards.
3. Fixes were not reaching the binary under test. Tauri embeds frontendDist at
   compile time, but Cargo does not track dist-desktop/ as a build input. Rebuilding the
   frontend and rebuilding the app produced a binary carrying the previous bundle, with
   no warning. Three rounds of fixes were built, installed to /Applications, launched,
   and observed still-broken — because none of them were in the binary being launched.
4. There was no way to see the running app. This shell has no macOS Screen Recording
   or Accessibility permission, so screenshots come back black. Verification depended on
   asking a human to look, which is slow and is how (3) survived three rounds.

The root cause

One line of validation in Better Auth:

Invalid base URL: tauri://localhost. URL must include 'http://' or 'https://'

createAuthClient() infers its base URL from window.location.origin when none is given.
On the web that is https://… and everything is fine. Under Tauri the origin is the custom
scheme tauri://localhost, which better-auth/dist/utils/url.mjs:36 rejects for any
protocol that is not http:/https:.

The critical detail is when it throws. authClient is a module-scope const, so the
throw happens while src/lib/auth/client.ts is being evaluated — during dynamic import
of the route chunk, before a single component renders. The router boundary catches it, and
the entire app is replaced by the fallback.

The sibling app agent-brain-ui shares this stack and works, which made the difference
look mysterious. It is not: its root route renders its app shell directly and never touches
auth at boot. ForgeNotes' AppShell calls authClient.useSession() on mount, so ForgeNotes
walks into the validator and agent-brain-ui does not.

What this PR actually does

src/lib/auth/base-url.ts (new) + src/lib/auth/client.ts

Supplies an explicit baseURL only when the page origin is not http(s):

export function resolveAuthBaseURL(protocol: string | undefined): string | undefined {
  if (protocol === "http:" || protocol === "https:") return undefined;
  return protocol ? DESKTOP_AUTH_ORIGIN : undefined;
}

undefined means "let Better Auth infer it as before". Every web origin — production, dev,
and the Grok live preview — takes that branch and is bit-for-bit unchanged in behaviour.
Only tauri:// gets an override.

This edits a file CLAUDE.md marks frozen. src/lib/auth/* is pre-wired template
code and the rule exists because rewriting it breaks live-preview sign-in in ways that
are slow to diagnose. There is no other correct location: the throw is inside
createAuthClient, at module scope, in that file. The change is two lines, purely
additive, and inert on every origin the freeze is there to protect. Flagging it
explicitly rather than letting it pass unnoticed in a diff.

src/router.tsx + src/lib/report-client-errors.ts

Wires error reporting to defaultOnCatch, which is the router boundary's own catch point
and receives exactly the error the boundary is about to hide. The pre-existing window
listeners stay for genuinely uncaught errors; they are simply blind to this class.

scripts/build-desktop.mjs

Bumps the mtime of a tracked Rust source at the end of the build, forcing Cargo to
re-embed. One extra compile of one crate, and problem (3) above cannot recur.

Housekeeping

• Untracks 249 .vercel/ build artifacts committed by an earlier git add -A — the same
  mistake PR Untrack dist-desktop — build artifact committed by accident #23 undid for dist-desktop/. Both are now gitignored.
• Adds dist-desktop/** and src-tauri/target/** to the ESLint ignore list. 10,468 of
  the 10,990 reported "errors" were minified bundles. The real count is 1 error (the
  known pre-existing rules-of-hooks at AppShell.tsx:78) and 12 warnings.

Corrects a claim that was wrong

An earlier commit added safe-storage.ts with a docstring asserting that WebKit denies DOM
storage to tauri://localhost and that this "crashed the desktop build on boot for every
user, every time." That is false. Storage was measured working in that webview:

{"storage": "works", "origin": "tauri://localhost", "secureContext": true}

Denying storage synthetically reproduced the same error-boundary text, and a reproduction
that matched the symptom was mistaken for finding the cause. The wrapper is kept — it is
real hardening for Safari private browsing and partitioned iframes — but the comments in
safe-storage.ts, store.ts, and safe-storage.test.ts now say what is actually true.

How it was verified

Not by inference. The debug binary was rebuilt with the mcp-bridge feature so it runs
under the asset protocol (tauri://localhost, the real packaged code path — not the
dev server, which npm run desktop:mcp reuses and which therefore cannot reproduce this at
all), then queried directly:

Check	Before	After
document.body.innerText	Something went wrong! …	full workspace chrome
[data-block-id] count	0	20
<button> count	2	97
sidebar present	no	yes
boundary errors on stderr	1	0

Plus: npm run typecheck clean; npx vitest run 43/43 across 6 files, including 4 new
tests on resolveAuthBaseURL; release bundle and the copy in /Applications both verified
by binary inspection to embed the current entry chunk (index-ChMLEjem.js).

The human confirmed the same error text independently from a screenshot before the fix
landed, which is what ruled out an artifact of the measurement setup.

Deliberately out of scope

• Auth does not function on desktop. The packaged app has no server, so
  /api/auth/* has nothing to answer it. The base URL is set to http://127.0.0.1:8080,
  which works when a dev server is up and otherwise fails the session fetch gracefully —
  the app renders signed-out instead of dying. Making desktop auth actually work needs a
  real decision about where the desktop backend lives.
• The .dmg is unsigned and un-notarised. Gatekeeper will block it on any other Mac.
• The two remaining lint findings (rules-of-hooks, unused-var warnings).
• mounts-store.ts and ai/settings-store.ts still use raw localStorage. Harmless given
  the finding above; worth aligning if the wrapper is ever load-bearing.

Ticket glossary

Ticket	What it is	Status
01KZ4FQNVT4N2H3XV0QYY9X1SS	Desktop window blanks: Better Auth rejects tauri://	Closed by this PR
01KZ4D4P3YE5H94JXVZKCA08YY	Desktop ships a dead placeholder — SSR build has no static entry	Closed by this PR
01KZ3Z46SDWDGVD3CFZ0Z1S9FB	Parent: desktop packaging path (v0.3.1)	In progress

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