fix(react): isolate loader data from activity context by ENvironmentSet · Pull Request #736 · daangn/stackflow

ENvironmentSet · 2026-07-23T04:03:43Z

Problem

The built-in loaderPlugin in @stackflow/react stores loader results (as Promises) in the shared activityContext.loaderData. Since activityContext is shared across all plugins and is included verbatim in StackSnapshot events:

There is no per-plugin key ownership/namespace, so the loaderData key can collide with other plugins' or users' data and be silently overwritten depending on execution order.
Runtime-only data (Promises, loader return values) leaks into Snapshots, breaking the plain-data / round-trip contract of StackSnapshot.

Solution

Loader runtime state now lives in plugin-owned storage, fully outside activityContext:

Each core-store loaderPlugin instance owns private Maps keyed by the entering domain-event ID, isolating multiple Stackflow/SSR store instances and keeping separate loader generations when replace() reuses an activity ID (including a rendered generation plus a queued paused replacement).
wrapActivity provides the promise for activity.enteredBy.id to useLoaderData through an internal React Context — no render-phase mutation, no effects.
Lifecycle cleanup drops exit-done generations, retains queued paused generations, and removes staged data for prevented actions.
loaderPlugin no longer reads or writes activityContext.loaderData; values placed there by users or other plugins pass through unchanged (and are no longer consumed by useLoaderData).

No @stackflow/core public contract changed. Existing public surfaces are preserved: useLoaderData, SSR initialLoaderData, core v3 load (restore) path with loader re-execution and deferred resolution, pausedEvents handling, pause/resume loading behavior, and the lazy shouldRenderImmediately path.

Verification

yarn typecheck (all workspaces), @stackflow/react / @stackflow/plugin-stack-persistence / demo builds — PASS
Existing suites: @stackflow/core (14 suites / 84 tests), @stackflow/plugin-history-sync (7 suites / 52 tests) — PASS
Runtime harness covering: fresh loader + real useLoaderData render, foreign-key collision isolation, Snapshot JSON safety, core v3 restore round-trip, SSR initialLoaderData, plugin-stack-persistence save/load round-trip, paused same-ID replacement generations, pending loader + lazy pause/resume, independent stores reusing identical IDs, exit-done / prevented-action cleanup — all PASS. The harness rejects any Promise found in captured Snapshot records and confirms deliberately-planted foreign activityContext.loaderData values are preserved for core/persistence while useLoaderData returns only the plugin-owned value.

Closes FEP-2613

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changeset-bot · 2026-07-23T04:03:46Z

🦋 Changeset detected

Latest commit: 63fd197

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@stackflow/react	Patch

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coderabbitai · 2026-07-23T04:04:49Z

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Reviewing files that changed from the base of the PR and between 87286ba and 63fd197.

📒 Files selected for processing (1)

integrations/react/src/loader/loaderPlugin.tsx

🚧 Files skipped from review as they are similar to previous changes (1)

integrations/react/src/loader/loaderPlugin.tsx

📝 Walkthrough

Summary by CodeRabbit

Bug Fixes
- Improved loader data handling across navigation, activity transitions, and page lifecycle changes.
- Prevented loader promises and returned values from being retained in activity context or captured navigation snapshots.
- Kept resolved loader data accessible via useLoaderData, including deferred and async loader scenarios.
New Features
- Added a dedicated loader-data React context with a useLoaderDataPromise accessor.
Chores
- Added a patch release note documenting the updated loader data behavior.

Walkthrough

Loader results move from activity context into loader-plugin-owned maps and are exposed through a React context. Initialization, restoration, navigation preloading, promotion, and cleanup now use event- and activity-keyed runtime state.

Changes

Loader data isolation

Layer / File(s)	Summary
Loader data context contract `integrations/react/src/loader/LoaderDataContext.tsx`, `integrations/react/src/loader/useLoaderData.ts`	Adds a context-backed loader promise provider and updates `useLoaderData` to resolve loader data from that context.
Event-keyed loader state `integrations/react/src/loader/loaderPlugin.tsx`	Stores loader promises and deferreds by event or activity identifier, provides data through `LoaderDataProvider`, and updates initial and restored-stack resolution.
Navigation staging and cleanup `integrations/react/src/loader/loaderPlugin.tsx`, `.changeset/fep-2613-isolate-loader-data.md`	Stages preloaded data in runtime state, pauses and resumes navigation actions, promotes retained data, cleans stale entries, and records the patch release.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Sequence Diagram(s)

sequenceDiagram
  participant RouteNavigation
  participant loaderPlugin
  participant LoaderDataProvider
  participant Activity
  RouteNavigation->>loaderPlugin: Start route preload
  loaderPlugin->>loaderPlugin: Pause actions
  loaderPlugin->>loaderPlugin: Store resolved loader data
  loaderPlugin->>loaderPlugin: Resume actions
  loaderPlugin->>LoaderDataProvider: Provide loader promise
  LoaderDataProvider->>Activity: Render activity with loader context
  loaderPlugin->>loaderPlugin: Remove staged data on next microtask

Possibly related PRs

daangn/stackflow#732: Both update loader-plugin deferred resolution and load-path handling for snapshot restoration.
daangn/stackflow#738: Both modify createBeforeRouteHandler and runtime loader-data staging in loaderPlugin.tsx.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: isolating loader data from activity context.
Description check	✅ Passed	The description accurately describes the PR's purpose and the loader-state isolation changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Commit unit tests in branch feature/fep-2613

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pkg-pr-new · 2026-07-23T04:06:43Z

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cloudflare-workers-and-pages · 2026-07-23T04:07:22Z

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coderabbitai Bot mentioned this pull request Jul 24, 2026

fix: skip loader work for prevented actions (FEP-2635) #738

Open

ENvironmentSet added 2 commits July 24, 2026 18:03

fix(react): isolate loader data from activity context (FEP-2613)

9d628e7

chore: add FEP-2613 changeset

87286ba

ENvironmentSet force-pushed the feature/fep-2613 branch from 3058ce7 to 87286ba Compare July 24, 2026 09:03

ENvironmentSet added 2 commits July 24, 2026 18:28

fix(react): retain loader data for deferred renders (FEP-2613)

a377c26

fix(react): invalidate canceled loader staging (FEP-2613)

63fd197

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