[fstagni]

Summary

Cherry-pick of #814 for rel-v5r0 (same fix, applies cleanly - UPHandler.py is identical on both branches; #810/#811 equivalents are already in).

The v6.0.7 JSON migration broke the state save/load round trip in UPHandler:

 web_saveAppState(state)        # browser sends state as a JSON text (Ext.JSON.encode)
-  DEncode.encode(state)        # opaque wrap: decode + json.loads gave the structure back
+  json.dumps(state)            # double-encoded: JSON of a JSON string

 _safeDecode(raw)
-  json.loads(DEncode.decode(raw)[0])   # historic: str -> dict
+  DEncode.decode(raw)[0]               # regression: returns the JSON text as str

UP/listAppState therefore returned {name: "<json string>"} instead of {name: {...}}. In the frontend, oprVerifyDataStructure() throws on a string, the callback building the desktop tree never fires, and the "My Desktops" node is never created. Users with no saved desktops under the logged-in group still see the (empty) node - matching the reported symptom. Shared desktops kept working because their listing is metadata only. web_changeView was broken too (rejected every desktop with "Invalid desktop state format").

Changes:

• web_saveAppState: store the state verbatim when it is already a JSON text
• _safeDecode: unwrap redundant JSON string layers, restoring the historic json.loads(DEncode.decode(...)[0]) behavior. States saved with the broken versions decode correctly and self-heal on their next save - no DB migration needed
• add regression tests covering all storage generations (legacy DEncode, double-encoded v6.0.7/8, current)

Evidence

• Before: _safeDecode returned str for every stored desktop generation -> oprVerifyDataStructure() TypeError -> "My Desktops" missing
• After: all three generations round-trip to the original dict:

legacy DEncode         -> dict ok=True
double-encoded v6.0.7  -> dict ok=True
current                -> dict ok=True

Note: the pytest run requires the DIRAC release matching this branch (rel-v5r0's WebHandler imports DIRAC.Core.Tornado.Server.TornadoREST, removed in newer DIRAC); the decode logic itself was verified against all storage generations.

Merge Danger

Door: two-way - pure backend decode/encode fix, no schema change, no data migration; stored data is untouched and self-heals on save.

Blast Radius: all users' saved desktops and application states (My/Shared Desktops, changeView). Shared-desktop metadata listing is unaffected.

[fstagni]

Closing: the regression this fix addresses (introduced by the JSON-migration backport #811) was never released - v5.0.15 (49ee635) predates it, and no further v5r0 release is planned. The fix for the v6.0.x line is in #814 (integration).