Reads the `__nextInstantNav` marker from the error to pick the right
overlay copy for the blocking-route family:

- Headline: "Next.js encountered runtime/uncached data during a
  navigation." (in-nav) vs. "during the initial render." (initial).
- Explanation: "This prevents the navigation from being instant..." vs.
  the default "prevents the route from being prerendered..." string.

Adds `BLOCKING_ROUTE_NAVIGATION_EXPLANATION` next to `EXPLANATIONS` in
`instant-guidance-data.ts` so all overlay copy stays in one place.

Also renames the legacy `'navigation'` value of `GuidanceVariant` to
`'dynamic'` — the original name meant "uncached data" (from #92638) and
collides with the new in-navigation concept. The new shape is
`'runtime' | 'dynamic'` for what kind of data is accessed, plus an
orthogonal `inNavigation: boolean` for the phase.

Co-authored-by: Cursor <cursoragent@cursor.com>

Object markers on the Error don't survive RSC serialization
(`__NEXT_ERROR_CODE` already has a side-channel Map for this same
reason), so the previous `__nextInstantNav` property was getting
stripped before the dev overlay ever saw it.

Switches detection to two structural substrings already present in the
user-facing copy:

- \`accessed under \`<Suspense>\`\` — only emitted by the in-navigation
  body factories. The mirrored SSR factories say \`accessed outside of
  \`<Suspense>\`\`, so the two are unambiguous.
- \`Could not validate \`unstable_instant\`\` — already used to detect
  wrapper errors (E1082 / E1112 / E1113 / E1118), tied to the API name
  rather than phase wording.

Drops the marker helper from `blocking-route-messages.ts`.

Co-authored-by: Cursor <cursoragent@cursor.com>

The dev overlay renders in a separate React root mounted at the document
body (via `createRoot(container)` in `dev-overlay.browser.tsx`), so the
App Router's `PathnameContext` isn't in scope and `usePathname()` returns
`null` — making the previous `useClearInstantErrorsOnNav` effect a no-op.

Switches to a browser-level subscription: listen for `popstate` (back /
forward) and patch `history.pushState` / `history.replaceState` to detect
client navigations triggered by `next/link` and `router.push()`. Cleanup
restores the originals so the patch is scoped to overlay lifetime.

This matches the pattern other dev-overlay code already uses for current
path (e.g. `route-info.tsx` reads `window.location.pathname` directly).

Co-authored-by: Cursor <cursoragent@cursor.com>

Co-authored-by: Cursor <cursoragent@cursor.com>

…/instant-nav-error-clear

The new `createRuntimeBodyErrorInNavigation` / `createDynamicBodyErrorInNavigation`
factories produce "encountered runtime data during a navigation" wording in
the dev overlay (via inNavigation substring detection in errors.tsx). Seven
inline snapshots in instant-validation-parallel-slots.test.ts locked in the
older "during the initial render" + E1221 / E1220 wording — flipped to the
new "during a navigation" + E1247 / E1246.

The eighth test in this file is left at canary state: it relies on PR #93770's
"expected segment was not rendered" message which currently bakes in a
test/tmp/next-test-… absolute path. That test is broken on canary HEAD
too (verified directly) — not a regression from this PR.

Co-authored-by: Cursor <cursoragent@cursor.com>

`instant-validation.test.ts` (28 snapshots) and
`instant-validation-parallel-slots.test.ts` (7 snapshots) had build-mode
inline snapshots that pinned the older `createRuntimeBodyError` /
`createDynamicBodyError` wording. Switched to the new in-navigation
factory output:

  - "encountered runtime data during the initial render."
  + "encountered runtime data during the initial render or a navigation."

  - "accessed outside of `<Suspense>` prevents the route from being
    prerendered, blocking navigation and leading to a slower user
    experience."
  + "accessed under `<Suspense>` prevents the route from being
    prerendered or the navigation from being instant, leading to a
    slower user experience."

Captured without NEXT_SKIP_ISOLATE so the test packed next.js as a
tarball (matching the CI build path); avoids leaking local
`../../../packages/next/dist/esm/...` stack frames into the snapshots.

Co-authored-by: Cursor <cursoragent@cursor.com>

The in-navigation body factories said "accessed under \`<Suspense>\`",
which contradicts the fix bullet that recommends wrapping in Suspense.
The actual problem is the same as the SSR factories: data accessed
*outside* a Suspense boundary, where the prerender / prefetchable
shell can't proceed without waiting. Aligned both InNavigation factories
to "accessed outside of \`<Suspense>\`" so the diagnostic matches the
SSR factories — only the consequence clause differs (still includes
"or the navigation from being instant").

Refactored the substring detection that distinguishes in-navigation
vs SSR variants into a single `isBlockingRouteInNavError` helper in
`shared.ts`, used by both `getInstantErrorRoute` (clear-on-nav) and
`getBlockingRouteErrorDetails` (overlay headline phase). Helper keys
off "or a navigation" which is still unique to the InNavigation factory
pair (the diagnostic clause is now shared).

Also narrowed `getInstantErrorRoute` to detect *only* body factory
errors — wrapper errors like "Could not validate \`unstable_instant\`"
are no longer cleared on navigation. They describe a validation
infrastructure failure rather than a fixable route-level mistake and
should stay in the redbox stack until the user addresses the cause.

Snapshot updates across `instant-validation.test.ts` (dev + build
modes) and `instant-validation-parallel-slots.test.ts` (dev + build
modes) reflect the new wording. Build-mode snapshots captured without
NEXT_SKIP_ISOLATE so the test packs Next.js as a tarball and produces
the same stack frame shape CI sees (avoids leaking local dist paths).

Co-authored-by: Cursor <cursoragent@cursor.com>

…nt-nav-error-clear

- Drop history.pushState/replaceState patching in favor of state.page
  from ACTION_DEVTOOL_UPDATE_ROUTE_STATE (cooperates with App Router's
  own history patching).
- Update errors.test.ts for new {inNavigation, variant: 'dynamic'} shape
  and add InNavigation factory cases.
- Bump E1246/E1247 -> E1249/E1250 in level-* and causes tests after the
  factory wording change.

Co-authored-by: Cursor <cursoragent@cursor.com>

- Restore the 13-space indent on `Unrendered segment(s):` paths in dev
  inline snapshots (got stripped during the earlier wording sweep).
- Use the stable `app/...` prefix instead of the non-deterministic
  `test/tmp/next-test-<timestamp>-<rand>/...` path that crept into one
  parallel-slots snapshot.

Co-authored-by: Cursor <cursoragent@cursor.com>

`state.page` is the resolved URL (e.g. `/foo/123`), but an instant error's
embedded `Route "..."` uses the route pattern (`/foo/[param]`). Firing
the clear action on the initial '' → page transition would always wipe
dynamic-route errors before the redbox could open. Treat the first
non-empty page as the baseline and only dispatch on subsequent changes.

Co-authored-by: Cursor <cursoragent@cursor.com>

The SSR `createRuntimeBodyError` lists the Suspense placeholder first
(the most general fix) followed by `generateStaticParams`. The
in-navigation variant had them flipped, so the top-of-list suggestion
was the narrower one (only applies to dynamic-param routes). Reorder
the in-nav factory to match SSR, and refresh the build-mode CLI
snapshots and the runtime-body in-nav error code (E1250 → E1251).

Co-authored-by: Cursor <cursoragent@cursor.com>

The earlier wording sweep on the level-* tests preserved the pre-existing
2-space-shy indent on the `code` and `description` lines, so Jest's diff
reported a whitespace-only mismatch even though the values agreed. Match
them to the sibling JSON keys (13 spaces).

Co-authored-by: Cursor <cursoragent@cursor.com>

The previous patch overshot to 13 spaces in tests where the snapshot
braces sit two columns shallower (so sibling keys are at 11). Auto-align
each `code`/`description` line to the indent of the next sibling key.

Co-authored-by: Cursor <cursoragent@cursor.com>

`trackDynamicHoleInNavigation` is also reached during the build-time
prerender pass, so the CLI build error now reads "during the initial
render or a navigation" with the matching consequence clause. Update
the build-mode snapshots in `instant-validation-build` and the four
`instant-validation-level-*` tests to match.

Co-authored-by: Cursor <cursoragent@cursor.com>

…ording

The earlier wording sweep also touched the 4 \`without-root-suspense\`
E1220 snapshots, which come from the SSR factory (initial-render path)
and should keep "during the initial render." Restore the SSR wording
on those four.

Co-authored-by: Cursor <cursoragent@cursor.com>

…/instant-nav-error-clear

`Route "<path>":` in the error message is the route template
(e.g. `/foo/[slug]`), while `state.page` is the resolved URL
(e.g. `/foo/123`). Equality matching dropped SSR-streamed errors
on the destination page during navigation for any dynamic route.

Convert the template to a regex so the clear-on-nav reducer keeps
errors whose template matches the page the user just landed on.

…/redesign-unrendered-segment-overlay

# Conflicts:
#	packages/next/src/next-devtools/dev-overlay/container/errors.tsx
#	packages/next/src/next-devtools/dev-overlay/shared.ts
#	test/e2e/app-dir/instant-validation/instant-validation-parallel-slots.test.ts
#	test/e2e/app-dir/instant-validation/instant-validation.test.ts