---
title: Failure Boundary
status: draft
maturity: hypothesis
families: [quality, composition]
scales: [L5, L6]
admission: research-candidate-only
---

# Failure Boundary

Context: a failing region should not remove unrelated useful work. Continuity
competes with the cost of partial-state recovery and boundary coordination.

Proposed solution: define which failures a boundary contains, replace the affected
region with usable feedback, and give recovery an explicit reset/retry contract.
Keep required navigation and recoverable intent outside the failing subtree when
appropriate. If containment itself fails, define the next enclosing recovery path.

Result: some work can continue; shared state corruption or global runtime failure
may still cross the boundary. Resetting presentation does not undo remote effects.
Never replay a write merely because a region remounted. Distinguish expected domain
rejection and network errors from uncaught rendering faults.

Evidence: B05 locates React's rendering-error boundary and documented exclusions;
this proposal does not claim it catches every asynchronous or event-handler error.
Alternative: fail the entire task when partial continuation would mislead users.
A fallback is a product state that needs accessible controls, not just logging.

Proposed relations: [Mutation Outcome Tracking](MutationOutcomeTracking.md) handles
uncertain writes separately; [Focus Return](FocusReturn.md) applies to modal dismissal,
not automatically to every error replacement.

Next test: inject render, event-handler, network and fallback failures separately;
record which are contained and whether retry duplicates an accepted operation.

Evidence locators: [breadth review](../reviews/PatternBreadthExpansion.md).
All relations are research proposals; no canonical identity or admitted graph edges.
The next test is planned, not executed. Known uses of the complete proposed contract
have not been verified in this investigation.

## Executed partial evidence — 2026-09-26

[Boundary experiment](../reviews/BoundaryRecoveryExperiment.md) X01–X04 runs real
React 19.3.0 in a browser fixture. A render fault stays inside its region; an event
handler error does not; a handled 503 uses explicit request state; a broken fallback
reaches the enclosing boundary. These are bounded mechanism observations, not
production recurrence or evidence for mutation rollback. Retain hypothesis maturity.