fix(bigtable): avoid triggering per-RPC credential session fallback on default call context - #14961

…les and verify VirtualRpc traffic (#14963)

### Summary
- Make `bigtable-session-it` a composable Maven profile that sets
`bigtable.internal.client-config-override-use-default=true` and
`bigtable.internal.client-config-override=session_configuration {
session_diversion_configuration { global_diversion { session_load: 1.0 }
} }` so it can be combined with `bigtable-cfe-it` (`-P
bigtable-cfe-it,bigtable-session-it`) or `bigtable-directpath-it` (`-P
bigtable-directpath-it,bigtable-session-it`).
- Scope `bigtable-cfe-it` failsafe `<includes>` to
`com.google.cloud.bigtable.data.v2.it.*IT` (matching
`bigtable-directpath-it`), which includes `SessionIT` when
`bigtable-session-it` is active (and skips `SessionIT` via `Assume` when
`bigtable-session-it` is not active).
- Update `.kokoro/presubmit/bigtable-integration-session.cfg` to compose
`-P bigtable-cfe-it,bigtable-session-it,enable-verbose-grpc-logs`.
- Update `SessionIT`:
- Chain `PeerInfoCapturingInterceptor` onto any existing
`channelConfigurator` from `CloudEnv` (`REQUIRE_CFE` /
`REQUIRE_DIRECT_PATH`) instead of overwriting it.
- Assert that `readRow` and `mutateRow` actually send
`SessionRequest.virtual_rpc` messages over `OpenTable` and do not fall
back to classic `ReadRows`/`MutateRow` RPCs (previously `SessionIT` only
checked `bigtable-peer-info` headers from background `OpenTable` stream
establishment, allowing silent fallback to classic RPCs to go
undetected).
- Assert the expected `PeerInfo.TransportType`
(`TRANSPORT_TYPE_SESSION_DIRECT_ACCESS` under `REQUIRE_DIRECT_PATH`,
`TRANSPORT_TYPE_SESSION_CLOUD_PATH` under `REQUIRE_CFE`).

### Related PRs
- Depends on #14961 (expected to fail `SessionIT` on `main` until #14961
is merged).

---------

Co-authored-by: Mattie Fu <mattiefu@google.com>

🤖 I have created a release *beep* *boop*
---


<details><summary>1.97.0</summary>

##
[1.97.0](v1.96.0...v1.97.0)
(2026-11-12)


### ⚠ BREAKING CHANGES

* **shopping-merchant:** remove discontinued Merchant API v1beta
([#14942](#14942))

### Features

* **bigquery-jdbc:** adds BigQuery graph integration to DatabaseMetadata
methods
([#14930](#14930))
([950b81b](950b81b))
* **gax:** implement resumable upload session resumption
([#14677](#14677))
([24728d6](24728d6))
* **grpc-gcp:** add built-in channel_count metric for client library
pools
([#14947](#14947))
([712f043](712f043))
* **grpc-gcp:** add built-in channel_load metric for client library
pools
([#14985](#14985))
([9f87888](9f87888))
* **shopping-merchant:** remove discontinued Merchant API v1beta
([#14942](#14942))
([2947dfd](2947dfd))
* **storage:** add StorageErrorTypeMapper for standard metrics
([#14694](#14694))
([a9ac393](a9ac393))
* **storage:** add StorageMetricsContext for operation metrics state
([#14728](#14728))
([edea395](edea395))
* **storage:** wire logical operation metrics in Retrying and
StorageOptions
([#14695](#14695))
([589c66c](589c66c))
* update API sources and regenerate
([#14958](#14958))
([75944f3](75944f3))


### Bug Fixes

* **auth:** verify public/private key match with retries in mTLS
keystore loading
([#14829](#14829))
([096dbd6](096dbd6))
* **bigquery:** set QueryResultsFormat.ARROW in QueryArrow sample
([#14960](#14960))
([c98e7c3](c98e7c3))
* **bigtable:** avoid triggering per-RPC credential session fallback on
default call context
([#14961](#14961))
([eb06d2c](eb06d2c))
* **bigtable:** copy Metadata per GetClientConfiguration call
([#14950](#14950))
([278fe2f](278fe2f))
* **bigtable:** disable SwitchingChannelPool when
ChannelPoolConfiguration is empty
([#14911](#14911))
([fa24702](fa24702))
* **bigtable:** handle empty SessionPoolConfiguration in SessionPoolImpl
and PoolSizer
([#14912](#14912))
([cc7b235](cc7b235))
* **bigtable:** replace SessionPoolImpl Watchdog with per-session
closeTimeout
([#14977](#14977))
([a15acfb](a15acfb))
* **spanner-jdbc:** report database default isolation level
([#14929](#14929))
([7e7595a](7e7595a))
* **spanner:** fix PG SHOW isolation level statements
([#14904](#14904))
([bc917ed](bc917ed))


### Dependencies

* bump grpc to 1.85.1, opentelemetry to 1.67.0, and guava to 33.7.2-jre
([#14957](#14957))
([1a27a00](1a27a00))
* bump guava to 33.7.1-jre and jspecify to 1.0.1
([#14937](#14937))
([1441527](1441527))


### Documentation

* **spanner:** update CHANGELOG.md for java spanner releases
([#14935](#14935))
([956681e](956681e))
* **storage:** add Rapid Cache samples
([#14886](#14886))
([e714f62](e714f62))
</details>

---
This PR was generated with [Release
Please](https://github.com/googleapis/release-please). See
[documentation](https://github.com/googleapis/release-please#release-please).

---------

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>