feat(odm): enable on-demand migration by default (#7089)

* feat(odm): enable on-demand migration by default

The module switch RUSTFS_ON_DEMAND_MIGRATION_ENABLED now defaults to true,
so the feature is reachable without an opt-in; setting it to false still
keeps the module out of the read path entirely. A bucket without an
on-demand-migration.json is never resolved by the runtime and makes no
source call, so the flip changes nothing for unconfigured buckets.

The admin plane now reads the switch through the predicate published by
module_switches.rs instead of its own duplicated env constant; the
behaviour (an environment read per call) is unchanged.

* test(e2e): wire three on-demand migration cases into e2e-smoke

The PR smoke lane gains one case per user-visible contract: a GET miss
that pulls and persists, a HEAD miss that answers from the source and
stores nothing, and the admin config/status pair that must redact the
source secret. The HEAD case did not exist outside the nightly
real-source lane, so it is added to get_basic_test.

Measured on darwin: the lane goes from 168 tests in 101.98 s to 171
tests in 101.92 s, since the three cases overlap the lane's existing
work. The darwin selection digests for e2e-smoke and e2e-full are
regenerated; the e2e-full linux digest still needs a Linux runner.

* docs(changelog): record the on-demand migration feature

.config/e2e-full-selection.txt

@@ -1,2 +1,2 @@
-sha256-darwin=efd7357af1e998134df7d01e0a10d7186898e47abbe86ae6ecb6aef1f8c58357
+sha256-darwin=a45665d370be1d49301599aff8fb3e1ffe349f47fd2e6734f844a850a15d08a6
 sha256-linux=86e69337ad1440252a2ee20a12063c989ed12442d3b1ddf9e9233acf0f2ec089

.config/e2e-smoke-selection.txt

@@ -1 +1 @@
-sha256=db9bd8cdcb0abe43461aa6b36499b17cabd4098e5b34e300b1a0f0d0f34d9884
+sha256=56a9de1c0f000954f1c9ec691e8f24cc2ee387e73cf8b0e684c2baf70317d910

.config/nextest.toml

@@ -394,6 +394,19 @@ test-group = 'ecstore-serial-flaky'
 # rustfs/rustfs#5169 disabled them) have PR-lane signal, not just merge-gate.
 # Single-node servers on random ports with isolated temp dirs — meets the
 # admission criteria unchanged.
+#
+# On-demand migration GA (backlog#2163 ODM-16): three named cases join the
+# lane, one per user-visible contract of the feature — a GET miss that pulls
+# the object and persists it locally, a HEAD miss that answers from the source
+# and stores nothing, and the admin config/status pair that must redact the
+# source secret. Each spawns one single-node rustfs server plus the in-process
+# fake S3 source (`fake_s3_target`, already in the first clause), so they meet
+# the admission criteria unchanged; measured at 15.8 s / 15.8 s / 15.9 s, which
+# is entirely the shared server startup and overlaps the lane's other tests.
+# The rest of `on_demand_migration::{get_basic,interaction,backfill,
+# harness_self}_test` stays in e2e-full and the fault / concurrency /
+# real-source modules stay in e2e-nightly; this is an allowlist, not a module
+# clause, so a new ODM test never lands here silently.
 [profile.e2e-smoke]
 default-filter = """
     package(e2e_test) & (
@@ -401,6 +414,7 @@ default-filter = """
         | test(/^replication_extension_test::(test_replication_check_succeeds_with_remote_target|test_replication_check_rejects_target_without_object_lock|test_set_remote_target_rejects_unversioned_source_bucket|test_replication_check_rejects_unversioned_source_bucket|test_replication_check_rejects_missing_replication_config|test_replication_check_rejects_invalid_bucket|test_set_remote_target_rejects_same_bucket_on_same_deployment|test_set_remote_target_rejects_unversioned_target_bucket|test_set_remote_target_update_requires_arn|test_set_remote_target_update_rejects_missing_target|test_set_remote_target_rejects_invalid_target_url|test_set_remote_target_rejects_self_signed_https_target_without_skip_tls_verify|test_set_remote_target_rejects_private_ca_https_target_without_ca_cert_pem|test_list_remote_targets_rejects_empty_bucket|test_list_remote_targets_rejects_invalid_bucket|test_remove_remote_target_rejects_missing_target|test_remove_remote_target_rejects_missing_arn|test_remove_remote_target_rejects_invalid_bucket|test_remove_remote_target_rejects_target_used_by_replication|test_delete_bucket_replication_removes_remote_target)$/)
         | test(/^reliant::lifecycle::/)
         | test(/^reliant::tiering::/)
+        | test(/^on_demand_migration::(get_basic_test::(get_miss_pulls_inline_and_serves_locally_afterwards|head_miss_answers_from_the_source_without_persisting)|interaction_test::test_odm_admin_config_is_redacted_and_status_counts_match_the_source)$/)
     )
 """
 fail-fast = false