Edit scheduled purchase fails with 'Failed to load plan details' (Planned 6.2) #773

Symptom (Planned Purchases 6.2)

Clicking the "Edit" button next to a scheduled purchase fails immediately with "Failed to load plan details".

Two issues here

1. Bug: the load itself fails. Find the network call (likely GET /api/plans/<id> or GET /api/purchase-executions/<id>/plan) and fix the 4xx/5xx that the frontend is surfacing.
2. Design question: should Edit on a scheduled purchase let the user edit the scheduled purchase (this one execution) or the entire plan it belongs to? Document the answer in this issue; current UI is ambiguous.

Acceptance (V1, just fix the load failure)

• Clicking Edit on a scheduled purchase no longer shows "Failed to load plan details".
• The modal opens with the plan details loaded.
• Add a backend test for the failing endpoint case the bug uncovered.
• Comment in this issue with the design question; do NOT silently change behavior beyond fixing the load.

Source

Planned Purchases 6.2, exploratory testing 2026-05-27.