docs(agents): make the structured-logging rule reachable and enforceable (#5828)

The RustFS event shape (`event`/`component`/`subsystem`/`result` + context,
message last) is specified only in
`.agents/skills/rustfs-logging-governance/SKILL.md`, and nothing routes a
change to it:

- `AGENTS.md`, which is what an agent actually loads by default, never
  mentions logging. Its only related line is "log unknown fields at `warn`"
  under Serde Safety, which is about level, not shape.
- The skill's `description` says "use when editing or reviewing RustFS logs",
  so a bugfix that adds one log line in passing — how most new log sites enter
  this repo — never matches it.
- `scripts/check_logging_guardrails.sh` is a blocklist: 500+ `rg -F` literals
  that retire log lines which already shipped. It cannot see a newly written
  one. For `crates/ecstore/src/disk/local.rs` the only check is that
  `#[tracing::instrument]` is TRACE-only; `warn!`/`info!` shape is unchecked.

PR #5822 landed `warn!("heal rename_data: purging ... {:?} failed: {}", ...)`
in `disk/local.rs` — sentence-style, no fields, directly beside `info!(event =
EVENT_DISK_LOCAL_RENAME_REJECTED, component = ..., subsystem = ...)` — with
every check green. That is the gap, not an authoring mistake.

Close all three:

- `AGENTS.md`: a Logging section stating the field shape, the level policy,
  the reuse-the-file's-constants rule, and that it applies to any `tracing`
  macro added in passing, not only to log-focused changes.
- Skill `description`: trigger on adding or editing any `tracing` macro,
  naming the single-line-added-in-passing case explicitly.
- Guardrail: assert the event shape positively on the already-governed disk
  files — `error!`/`warn!`/`info!` must open with fields or a `target:`, never
  a bare string. Commented-out macros are excluded; `debug!`/`trace!` stay out
  of scope as targeted diagnostics. Self-test fixtures cover both directions.

`crates/ecstore/src/disk/mod.rs` carried the one live violation in that file
set (`conv_part_err_to_int`), so it is converted here; the guardrail would
otherwise fail on an untouched file.

Verification:
- `./scripts/check_logging_guardrails.sh` — passes
- Negative control: re-inserting PR #5822's exact `warn!` line into
  `disk/local.rs` makes it exit 1 pointing at that line
- `cargo fmt -p rustfs-ecstore -- --check`, `cargo check -p rustfs-ecstore`

scripts/check_logging_guardrails.sh

@@ -842,6 +842,60 @@ for file in "${disk_logging_files[@]}"; do
   fi
 done
 
+# `forbidden_patterns` above only retires log lines that already shipped, so a
+# newly written sentence-style log passes every check in this script — which is
+# how one reaches review in the first place (PR #5822 added
+# `warn!("heal rename_data: purging ... {:?} failed: {}", ...)` to
+# disk/local.rs with CI green). Assert the RustFS event shape positively on the
+# file sets already governed here: error!/warn!/info! must open with fields
+# (`event = ...`) or a `target:`, never with a bare message string. debug! and
+# trace! stay out of scope — they are targeted diagnostics, not operator
+# events. Extend this list as more files are converted; it is deliberately
+# narrower than `checked_files`, which is only a blocklist surface.
+structured_event_files=(
+  "crates/ecstore/src/disk/mod.rs"
+  "crates/ecstore/src/disk/local.rs"
+  "crates/ecstore/src/cluster/rpc/remote_disk.rs"
+)
+
+# The leading class rejects `my_info!(` while still matching `tracing::warn!(`.
+sentence_style_log_pattern='(?:^|[^A-Za-z0-9_])(?:error|warn|info)!\(\s*"'
+
+for file in "${structured_event_files[@]}"; do
+  # Commented-out macros are dead code, not emitted events.
+  sentence_style_logs="$(rg -n -U "$sentence_style_log_pattern" "$file" | rg -v '^[0-9]+:\s*//' || true)"
+  if [[ -n "$sentence_style_logs" ]]; then
+    echo "❌ logging guardrail violation: error!/warn!/info! must lead with structured fields (event/component/subsystem) in $file" >&2
+    echo "$sentence_style_logs" >&2
+    exit 1
+  fi
+done
+
+# Keep the matcher honest in both directions.
+for fixture in \
+  'warn!("heal rename_data: purging stale destination data dir {:?} failed: {}", dst_data_path, err);' \
+  $'warn!(\n    "rename_data commit failed: {}",\n    err\n);' \
+  'tracing::warn!("conv_part_err_to_int: unknown error: {err:?}");' \
+  'info!("disk scan finished");'; do
+  if ! printf '%s\n' "$fixture" | rg -U "$sentence_style_log_pattern" >/dev/null; then
+    echo "❌ logging guardrail self-test failed: sentence-style log was accepted" >&2
+    echo "$fixture" >&2
+    exit 1
+  fi
+done
+
+for fixture in \
+  $'info!(\n    event = EVENT_DISK_LOCAL_RENAME_REJECTED,\n    component = LOG_COMPONENT_ECSTORE,\n    reason = "rename_all_data_path_failed",\n    "Disk local rename flow failed"\n);' \
+  'warn!(target: "rustfs::heal::manager", event = EVENT_HEAL_RETRY, "Heal retry admission decided");' \
+  'my_info!("not a tracing macro");' \
+  'debug!("list_dir raw {:?}", entries);'; do
+  if printf '%s\n' "$fixture" | rg -U "$sentence_style_log_pattern" >/dev/null; then
+    echo "❌ logging guardrail self-test failed: structured event was rejected" >&2
+    echo "$fixture" >&2
+    exit 1
+  fi
+done
+
 if rg -n -U 'debug!\([\s\S]{0,600}"Remote disk RPC started"' crates/ecstore/src/cluster/rpc/remote_disk.rs >/dev/null; then
   echo "❌ logging guardrail violation: successful remote disk RPC events must not be emitted at DEBUG" >&2
   exit 1