feat(get): harden codec streaming rollout (#3981)

* feat(get): consolidate GET performance optimization

Consolidated implementation of all GET performance optimizations into
a single, well-organized commit replacing the previous patch-on-patch
approach.

## Changes

### Configuration (set_disk/mod.rs)
- Consolidated all GET optimization flags into a single organized section
- Enabled by default: codec streaming, metadata early-stop, page cache reclaim
- Added codec streaming multipart flag (default: disabled)
- Added version-aware early-stop flag (default: disabled)
- Added adaptive duplex buffer sizing based on object size
- All flags use OnceLock caching with rollout percentage support

### Metadata Early-Stop (set_disk/read.rs)
- Delete marker early-stop when quorum agrees
- Version-aware early-stop for versioned GET requests
- MetadataQuorumAccumulator enhanced with:
  - delete_marker_votes tracking
  - requested_version_id and matching_version_votes tracking
  - version_early_stop_decision() method
- 6 new tests for version early-stop scenarios

### Codec Streaming (erasure/coding/decode_reader.rs)
- DualInFlight (2-stripe lookahead) enabled by default

### Decode Pipeline (erasure/coding/decode.rs)
- Stripe prefetch count configuration
- Bitrot-decode overlap configuration

### Disk Layer (disk/local.rs)
- O_DIRECT read configuration constants (preparation)

### Metrics (io-metrics/lib.rs)
- BytesPool acquisition/return metrics
- Metadata phase duration with early-stop label
- Total duration with reader_path label

### Diagnostics (diagnostics/)
- Early-stop reason constants
- Pool tier/outcome label constants

### Observability (.docker/observability/)
- 3 Grafana dashboards for GET optimization monitoring
- Prometheus alert rules (6 alerts: 3 critical, 3 warning)
- Updated README.md and README_ZH.md with usage docs

### Config (config/src/constants/runtime.rs)
- Page cache reclaim read enabled by default

## Environment Variables

| Variable | Default | Description |
|----------|---------|-------------|
| RUSTFS_GET_CODEC_STREAMING_ENABLE | true | Codec streaming base flag |
| RUSTFS_GET_CODEC_STREAMING_ROLLOUT_PCT | 100 | Codec streaming rollout % |
| RUSTFS_GET_CODEC_STREAMING_MULTIPART_ENABLE | false | Multipart codec streaming |
| RUSTFS_GET_METADATA_EARLY_STOP_ENABLE | true | Early-stop base flag |
| RUSTFS_GET_METADATA_EARLY_STOP_ROLLOUT_PCT | 100 | Early-stop rollout % |
| RUSTFS_GET_METADATA_VERSION_EARLY_STOP_ENABLE | false | Version-aware early-stop |
| RUSTFS_OBJECT_FILE_CACHE_RECLAIM_READ_ENABLE | true | Page cache reclaim |
| RUSTFS_OBJECT_DIRECT_IO_READ_ENABLE | false | O_DIRECT (preparation) |
| RUSTFS_GET_DECODE_STRIPE_PREFETCH_COUNT | 1 | Stripe prefetch |
| RUSTFS_GET_BITROT_DECODE_OVERLAP_ENABLE | false | Bitrot-decode overlap |
| RUSTFS_GET_CODEC_STREAMING_MAX_INFLIGHT | 2 | DualInFlight stripes |

## Rollback

All optimizations can be disabled via environment variables:
RUSTFS_GET_CODEC_STREAMING_ENABLE=false
RUSTFS_GET_METADATA_EARLY_STOP_ENABLE=false
RUSTFS_OBJECT_FILE_CACHE_RECLAIM_READ_ENABLE=false

Co-Authored-By: heihutu <heihutu@gmail.com>

* test(get): add stress test scripts for GET optimization validation

- quick-validate-get-optimization.sh: Quick 5-minute validation
- stress-test-get-optimization.sh: Full 30+ minute stress test
- README-stress-test.md: Usage documentation

Co-Authored-By: heihutu <heihutu@gmail.com>

* test(ecstore): align file cache reclaim defaults

* chore(deps): update redis and erasure codec

* test(ecstore): align decode fill policy default

* fix(get): wire codec streaming rollout gate

* perf(get): skip metrics-off codec timers

* test(get): capture codec streaming diagnostics

* test(get): add multipart fallback probe

* test(get): add encrypted fallback probe

* test(get): add compressed fallback probe

* test(get): add degraded read fallback probe

* test(get): cover remote fallback probe

* test(get): report warp request p99

* test(get): capture OTLP metric deltas

* perf(get): align codec streaming inflight default

* perf(get): reuse codec reader output buffers

* test(get): count codec reader fill starts

* perf(get): reuse codec reader fill worker

* perf(get): lazy init rustfs codec reconstruct

* test(get): cover rustfs codec source faults

* docs(get): record rustfs codec fallback scope

* feat(get): add multipart codec reader opt-in

* test(get): add multipart codec smoke option

* test(get): cover multipart codec degraded fallback

* perf(get): bound multipart codec eager setup

* test(get): satisfy codec hardening PR gate

---------

Co-authored-by: heihutu <heihutu@gmail.com>

crates/io-metrics/src/lib.rs

@@ -555,6 +555,21 @@ pub fn record_get_object_reconstruct_duration(path: &'static str, duration_secs:
     record_get_object_stage_duration(path, "reconstruct", duration_secs);
 }
 
+/// Record the reconstruction outcome for a GetObject reader path.
+#[inline(always)]
+pub fn record_get_object_reconstruct_outcome(path: &'static str, engine: &'static str, outcome: &'static str) {
+    if !get_stage_metrics_enabled() {
+        return;
+    }
+    counter!(
+        "rustfs_io_get_object_reconstruct_outcome_total",
+        "path" => path,
+        "engine" => engine,
+        "outcome" => outcome
+    )
+    .increment(1);
+}
+
 /// Record GetObject emit duration.
 #[inline(always)]
 pub fn record_get_object_emit_duration(path: &'static str, duration_secs: f64) {
@@ -715,6 +730,24 @@ pub fn record_get_object_fill_queued(path: &'static str, policy: &'static str, q
     histogram!("rustfs_io_get_object_fill_queued", "path" => path, "policy" => policy).record(usize_to_f64(queued));
 }
 
+/// Record that a background fill task was started for a GetObject reader path.
+#[inline(always)]
+pub fn record_get_object_fill_started(path: &'static str, policy: &'static str) {
+    if !get_stage_metrics_enabled() {
+        return;
+    }
+    counter!("rustfs_io_get_object_fill_started_total", "path" => path, "policy" => policy).increment(1);
+}
+
+/// Record that a persistent fill worker was started for a GetObject reader path.
+#[inline(always)]
+pub fn record_get_object_fill_worker_started(path: &'static str, policy: &'static str) {
+    if !get_stage_metrics_enabled() {
+        return;
+    }
+    counter!("rustfs_io_get_object_fill_worker_started_total", "path" => path, "policy" => policy).increment(1);
+}
+
 /// Record that a fill completed while the current output buffer still had unread bytes.
 #[inline(always)]
 pub fn record_get_object_fill_completed_before_output_drained(path: &'static str, policy: &'static str) {
@@ -1675,6 +1708,7 @@ mod tests {
         record_get_object_first_shard_read_duration("codec_streaming", 0.004);
         record_get_object_bitrot_verify_duration("codec_streaming", 0.005);
         record_get_object_reconstruct_duration("codec_streaming", 0.006);
+        record_get_object_reconstruct_outcome("codec_streaming", "legacy", "skip_data_complete");
         record_get_object_emit_duration("codec_streaming", 0.007);
         record_get_object_first_byte_latency("s3_handler", 0.008);
         record_get_object_full_body_latency("s3_handler", 0.009);
@@ -1696,6 +1730,8 @@ mod tests {
     #[test]
     fn test_record_get_object_fill_metrics() {
         record_get_object_fill_queued("codec_streaming", "single_inflight", 1);
+        record_get_object_fill_started("codec_streaming", "single_inflight");
+        record_get_object_fill_worker_started("codec_streaming", "single_inflight");
         record_get_object_fill_completed_before_output_drained("codec_streaming", "single_inflight");
         record_get_object_fill_waited_by_output("codec_streaming", "single_inflight", 0.0003);
         record_get_object_fill_cancelled_on_drop("codec_streaming", "single_inflight");
@@ -1770,6 +1806,7 @@ mod tests {
         record_get_object_first_shard_read_duration("codec_streaming", 0.004);
         record_get_object_bitrot_verify_duration("codec_streaming", 0.005);
         record_get_object_reconstruct_duration("codec_streaming", 0.006);
+        record_get_object_reconstruct_outcome("codec_streaming", "legacy", "legacy_called");
         record_get_object_emit_duration("codec_streaming", 0.007);
         record_get_object_first_byte_latency("s3_handler", 0.008);
         record_get_object_full_body_latency("s3_handler", 0.009);
@@ -1813,6 +1850,7 @@ mod tests {
         record_get_object_first_shard_read_duration("codec_streaming", 0.004);
         record_get_object_bitrot_verify_duration("codec_streaming", 0.005);
         record_get_object_reconstruct_duration("codec_streaming", 0.006);
+        record_get_object_reconstruct_outcome("codec_streaming", "rustfs", "rustfs_called");
         record_get_object_emit_duration("codec_streaming", 0.007);
         record_get_object_first_byte_latency("s3_handler", 0.008);
         record_get_object_full_body_latency("s3_handler", 0.009);