Dead path update skipping

SKILL: Dead Path Update Skipping

Domain: extensions-mcp
Trigger: Use when update candidates come from local paths that may disappear across checkouts, but existing materialized state should remain usable until a valid replacement exists. Source Pattern: Distilled from reviewed extension lifecycle and source-reconciliation patterns.

Core Method

Before running an update from a local path, verify that the declared path still exists. If the action is an update and the current materialized entry is still valid, skip the update rather than turning a transient path mismatch into a failed reinstall. This preserves the working materialized state in multi-checkout or ephemeral-path scenarios while still surfacing missing paths for truly absent entries.

Key Rules

• Only apply this skip to updates where a materialized entry already exists; missing entries should still surface real errors.
• Check path existence after normalization so you validate the exact path the reconciler would use.
• Record skipped updates distinctly from failures so operators know the existing entry was intentionally preserved.
• Limit the exception to local-path sources; remote sources need normal failure handling.
• Log the reason for the skip so future debugging can tell path drift from install breakage.

Example Application

If a developer switches away from a temporary worktree that contained a local marketplace path, keep the previously materialized marketplace entry instead of failing an update against the now-missing worktree path. The next valid local path or explicit reinstall can replace it later.

Anti-Patterns (What NOT to do)

• Do not attempt updates from dead local paths just to fail loudly; you destroy signal-to-noise while preserving nothing.
• Do not apply this rule to brand-new missing entries; if nothing working exists yet, the user needs the error.