[BUG] --configure-network writes invalid JSON (comma after the colon) when a postgres/mcp/web section's last member is a string with no trailing comma #2073

Component

Darling

Performance Monitor Version

stable v3.3.0 and dev @0eb7f52c (both)

SQL Server Version

not related

Windows Version

not related

Describe the Bug

On a minimal darling.json, --configure-network (the Store branch, or any branch that adds a network block to an existing section) produces invalid JSON and aborts with "the edited darling.json did not parse … No changes were written." - so LAN exposure can't be configured via the wizard for such a file.

Steps to Reproduce

1. Minimal config:

   { "postgres": { "managed": true, "dataDirectory": "E:\\Foo\\pg" }, "servers": [ { "name": "X", "host": "X", "auth": "sql", "username": "u", "encryptedPassword": "…" } ] }

2. Run PerformanceMonitor.Darling.Service.exe --configure-network, choose All (or just Store), enter a bind IP, CIDR, role.

3. At write time:

   Internal error: the edited darling.json did not parse (',' is an invalid start of a value. Path: $.postgres.dataDirectory | LineNumber: 3 | BytePositionInLine: 20.). No changes were written.

Expected Behavior

To work.

Actual Behavior

Not working.

Error Messages / Log Output

Screenshots

No response

Additional Context

Root cause: DarlingNetworkConfigEditor.InsertAsLastMember (Darling/PerformanceMonitor.Darling.Service/DarlingNetworkConfigEditor.cs:626-650) locates the previous member's end via PreviousCodeIndex(objectClose, objectOpen). PreviousCodeIndex skips StringLiteral regions, so when the last member's value is a string with no trailing comma (and no following commented template), it walks past the entire value and lands on the colon between key and value. needComma is then true and the comma is spliced in after the colon → "dataDirectory":, "…". It only bites a string-valued last member without a trailing comma; the shipped sample's postgres block ends "connectAs": "admin",, so the fixtures never exercise this shape.

Suggested fix: derive the comma-insertion point from the last member's actual value end (string-aware — e.g. reuse ValueEndFrom / enumerate members) instead of PreviousCodeIndex, which is blind to string values. Add a regression fixture with a minimal postgres/mcp/web block whose last member is string-valued and comma-less.