Cosmos: Track session tokens for Pre-Condition, Conflict and document NotFound failures

[JoasE]

Tracks the session token returned from a pre-condition, Conflict and NotFound failure, so subsequent reloads are ensured to read the latest document on re-load

Closes: #37942

[Copilot]

Pull request overview

Updates Cosmos provider session-token handling so that when an optimistic concurrency conflict occurs (HTTP 412), the session token from the failure response is captured—allowing subsequent reload/retry operations to read the latest document version under session consistency.

Changes:

• Track the Cosmos session token from CosmosException headers when wrapping a 412 (PreconditionFailed) into DbUpdateConcurrencyException.
• Preserve response headers when synthesizing a CosmosException for failed transactional batches, so session tokens are available to higher layers.
• Add a functional test asserting the session token is updated after an optimistic concurrency conflict (for both transactional and non-transactional save paths).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
test/EFCore.Cosmos.FunctionalTests/CosmosSessionTokensTest.cs	Adds a new test validating session-token updates after a concurrency exception.
src/EFCore.Cosmos/Storage/Internal/CosmosDatabaseWrapper.cs	Tracks session tokens from 412 responses before throwing DbUpdateConcurrencyException.
src/EFCore.Cosmos/Storage/Internal/CosmosClientWrapper.cs	Copies transactional batch response headers onto the constructed CosmosException to preserve session token info.

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[Copilot]

Pull request overview

Improves Cosmos session token tracking when an optimistic concurrency conflict occurs, ensuring the latest session token is recorded even when the failure comes from a transactional batch.

Changes:

• Track and persist the session token from CosmosException headers on HttpStatusCode.PreconditionFailed (optimistic concurrency conflict).
• Propagate transactional batch response headers into the created CosmosException so session tokens are available to the higher-level exception wrapper.
• Add a functional test verifying the session token is updated after a concurrency exception across different AutoTransactionBehavior modes.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
test/EFCore.Cosmos.FunctionalTests/CosmosSessionTokensTest.cs	Adds coverage to assert session token updates after a concurrency conflict and minor cleanup.
src/EFCore.Cosmos/Storage/Internal/CosmosDatabaseWrapper.cs	On concurrency conflicts, tracks the session token from the Cosmos response to support correct reload/retry behavior.
src/EFCore.Cosmos/Storage/Internal/CosmosClientWrapper.cs	Copies transactional batch response headers onto the thrown CosmosException so session token data isn’t lost on failure paths.

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[Copilot]

Pull request overview

Updates Cosmos session token handling to be more resilient by allowing null/whitespace tokens and by tracking session tokens from certain failure responses (and some read paths) to reduce the chance of subsequent stale reads.

Changes:

• Allow TrackSessionToken to accept string? and treat null/whitespace as “no-op”.
• Track session tokens on selected failure responses (e.g., conflict/precondition failed, some not-found cases) and refactor response processing in CosmosClientWrapper.
• Add/adjust unit + functional tests to cover the new session-token tracking behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
test/EFCore.Cosmos.Tests/Storage/Internal/SessionTokenStorageTest.cs	Updates unit tests to assert null/whitespace tokens are ignored (no longer throw).
test/EFCore.Cosmos.FunctionalTests/CosmosSessionTokensTest.cs	Adds functional coverage for session token updates after certain exceptions and not-found reads; removes unused usings/whitespace.
src/EFCore.Cosmos/Storage/Internal/SessionTokenStorage.cs	Makes TrackSessionToken nullable and ignores null/whitespace tokens.
src/EFCore.Cosmos/Storage/Internal/ISessionTokenStorage.cs	Updates interface contract to string? for session token tracking.
src/EFCore.Cosmos/Storage/Internal/CosmosClientWrapper.cs	Tracks session tokens from specific failure/read responses; refactors write/batch/read response handling.

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