feat(heal): incremental status cursors and typed overlap policy (HS-06) (#6206)

* feat(heal): incremental heal status cursors and typed overlap policy (HS-06)

Incremental results: every retained result item now carries a monotonic
sequence number. The status query accepts a client cursor (sinceSeq on
the admin wire, Option<u64> internally) and returns only newer items,
plus nextSeq (the next cursor) and minSeq (the oldest retained
sequence). A cursor that fell behind the 1024-item retention window is
flagged through the existing truncated signal together with minSeq so
the client can restart from it. Sequencing survives task completion:
the completion archive stores the seq-stamped window. None keeps the
exact legacy full-snapshot behavior, so existing clients see no change.

Typed overlap handling for admin starts: RUSTFS_HEAL_OVERLAP_POLICY
(merge default | minio_error). Under minio_error, an admin start whose
path overlaps an active or queued task rejects with typed
already-running / overlapping-paths admission reasons (surfaced through
reason_label in the admin error body, sharing the existing
OperationAborted site because the s3s footprint ratchet forbids new
s3_error! sites); an exact duplicate start rejects with
already-running instead of silently merging. Scanner/autoheal/
read-repair sources never take the rejection path.

forceStart semantics now match MinIO for admin requests: an admin
forceStart first cancels the overlapping active admin task, then
admits the replacement.

Wire: the heal-control Query command grows an optional sinceSeq
(defaulted and skipped when absent, so older peers stay compatible);
the admin handler accepts the sinceSeq query parameter; the local
channel query gains the same cursor.

Tests: seq monotonicity and incremental slicing, window slide moving
minSeq with lagging-cursor flags, overlap matrix (same/containing/
contained/disjoint x policy x source), forceStart cancel-then-admit,
and the completion-archive window handoff.

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

* style: fmt after main merge

---------

Co-authored-by: heihutu <heihutu@gmail.com>
Co-authored-by: zhi22915 <qiuzgang@gmail.com>

crates/common/src/heal_channel.rs

@@ -224,6 +224,13 @@ pub struct HealOpts {
 pub enum HealAdmissionDropReason {
     QueueFull,
     PolicyDropped,
+    /// HS-06: an admin heal start overlaps (same bucket with mutually
+    /// containing prefixes, or the same erasure set) an already running or
+    /// queued task. Only produced when RUSTFS_HEAL_OVERLAP_POLICY=minio_error.
+    AlreadyRunning,
+    /// HS-06: same as [`Self::AlreadyRunning`] but for paths that merely
+    /// contain (or are contained by) the active task's path.
+    OverlappingPaths,
 }
 
 impl HealAdmissionDropReason {
@@ -231,6 +238,8 @@ impl HealAdmissionDropReason {
         match self {
             Self::QueueFull => "queue_full",
             Self::PolicyDropped => "policy_dropped",
+            Self::AlreadyRunning => "already_running",
+            Self::OverlappingPaths => "overlapping_paths",
         }
     }
 }
@@ -317,6 +326,9 @@ pub enum HealChannelCommand {
     Query {
         heal_path: String,
         client_token: String,
+        /// Incremental result cursor (HS-06): only items with a sequence
+        /// greater than this are returned; `None` keeps the full snapshot.
+        since_seq: Option<u64>,
         response_tx: oneshot::Sender<Result<HealChannelResponse, String>>,
     },
     /// Cancel heal task
@@ -522,10 +534,21 @@ async fn receive_heal_channel_response(
 
 /// Send heal query request
 pub async fn query_heal_status(heal_path: String, client_token: String) -> Result<HealChannelResponse, String> {
+    query_heal_status_since(heal_path, client_token, None).await
+}
+
+/// Incremental heal query (HS-06): pass the client's last seen sequence
+/// number to receive only newer result items.
+pub async fn query_heal_status_since(
+    heal_path: String,
+    client_token: String,
+    since_seq: Option<u64>,
+) -> Result<HealChannelResponse, String> {
     let (response_tx, response_rx) = oneshot::channel();
     send_heal_command(HealChannelCommand::Query {
         heal_path,
         client_token,
+        since_seq,
         response_tx,
     })
     .await?;