[electricessence]

Fix: an AddParams member that the procedure (or the text) does not declare is no longer sent under a stale name left in the process-wide ArrayPool<string?>.

Resolving the names of an AddParams object keeps the name each parameter ends up with in an array rented from ArrayPool<string?>.Shared. For a member that matched nothing, the first pass moved on without writing its slot, and the later passes read the slot anyway: whatever an earlier renter had left there was sent as the parameter name (or made two unmatched members collide). A text command with @name markers takes the same path.

What changed

• ExpressiveCommandBase.Apply: the slot of an unmatched AddParams member is written (null: not sent) before it is read. One line. The clearing policy is unchanged (the used prefix is cleared on return).
• PooledNameSlotTests (7 tests): fill several arrays of the pool with a sentinel name and return them without clearing, between AddParams and the terminal, then run the command:
  • stored procedure, unmatched member only: sync and async;
  • stored procedure, matched and unmatched members: sync and async;
  • text command with @name markers, unmatched member: sync and async (ExpressiveCommand, ExpressiveDbCommand);
  • text command, only unmatched members: sync.
• Audit of every .Rent( site in Source/ (13): only this one read a slot before it was written. The other twelve write every slot they read (or hand the array to a caller under a documented contract). No other change.

Verification

Tests first, then the fix (two commits), Tests/Open.Database.Extensions.Core.Tests, net10.0 and net11.0.

• Before the fix: dotnet test Tests/Open.Database.Extensions.Core.Tests -c Release --filter FullyQualifiedName~PooledNameSlotTests --nologo: Failed 7, Passed 0 on both targets (for example Collection: ["@stale"] where an empty list is expected).
• With the fix, same command: Passed 7, Failed 0 on both targets.
• dotnet test Tests/Open.Database.Extensions.Core.Tests -c Release --nologo: net10.0 Passed 10200 of 10200; net11.0 Passed 10200 of 10200.
• dotnet test Tests/Open.Database.Extensions.Core.Tests -c Debug --nologo (so Debug.Assert fires): net10.0 Passed 10200 of 10200; net11.0 Passed 10199, Failed 1: SingleValueAllocationTests.ToArrayAndToListOfInt_AllocateNoMoreThanASelector(rows: 100) ("3890 B per call through the terminal, 1936 B by hand"). That test passes when run on its own (--filter FullyQualifiedName~SingleValueAllocationTests, Debug, net11.0, 12 of 12) and does not touch name resolution. It was not run against the unmodified tree.
• Release build and format check (style and analyzers): 0 warnings, 0 errors, no format findings.

Not done / decisions

• The one-off Debug failure above is reported, not fixed (an allocation measurement under a full parallel run). It is known to be intermittent on net11.0 and is being investigated separately, together with the other allocation test that fails on net11.0 Release only.
• Known and tracked separately: MappedQuerySelectTests.TheAsyncProjection_AllocatesNothingPerRow fails intermittently on net11.0 Release (it did in this branch's full gate run: 10199 of 10200 passed). It was already known before this branch and is in code this change does not touch.
• No clearing-policy change and no API change.
• Not changed: the tail of a longer rented object[] that GetValues leaves unwritten (documented on the public GetValues(record, ..., pool) methods; the library reads only the field count).

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