client-core: filter the ring's Debug/Trace lines to iris's own targets

Iris's phone report (docs/IRIS_TODO.md, 2026-09-07 night): the ring held
1339 lines and dropped 4050 more, almost all of it naga::front/wgpu_core/
jni logging at Debug unconditionally, because RingLogger accepted every
target at whatever level `log`'s own max was set to. The trace gate added
in 992c472 only covers iris's own debug! call sites, not a dependency's.

ring_accepts() is the one filter, applied in RingLogger::log rather than
per callsite: Info and above always rings, from anywhere (a dependency's
real warning is worth keeping); Debug and Trace ring only from `iris`/
`client_core` targets, and only while tracing is on. Tracing itself is
`iris::diagnostics::trace_enabled`, passed into RingLogger as a plain
`fn() -> bool` rather than called directly, since client-core sits below
iris and must not depend on it -- the same reason `inner` (the platform
logger) is already injected rather than chosen here.

Also adds LogRing::tail_text and COPY_REPORT_TAIL_LINES (150, named and
reasoned at the constant) for the next commit's Copy report trim.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

client-core/src/log_ring.rs

@@ -11,7 +11,7 @@
 //!
 //! Two consumers, both reading the same ring rather than each keeping
 //! their own: the bench app's `Copy report`/`Diagnostics` (which reads
-//! [`LogRing::to_text`] and [`LogRing::summary`]) and whatever hands the
+//! [`LogRing::tail_text`] and [`LogRing::summary`]) and whatever hands the
 //! log out of the process -- on Android, the `DevLogProvider` Dev Updater
 //! queries, which reads [`LogRing::since`] and [`LogRing::newest_seq`].
 //! That is why reading does not consume: a line already handed over must
@@ -32,6 +32,15 @@ use std::time::{SystemTime, UNIX_EPOCH};
 pub const DEFAULT_MAX_LINES: usize = 2000;
 pub const DEFAULT_MAX_BYTES: usize = 256 * 1024;
 
+/// How many of the ring's newest lines [`LogRing::tail_text`] includes.
+/// Sized for a phone's share sheet rather than for the ring itself: 150
+/// lines of `HH:MM:SS.mmm LEVEL target: message` is a few KiB, comfortably
+/// short of whatever made pasting the full (up to 2000-line) ring into a
+/// chat's message box laggy on Iris's phone. The full ring is still
+/// reachable through `devlog`'s provider, so this only bounds what a
+/// report inlines.
+pub const COPY_REPORT_TAIL_LINES: usize = 150;
+
 /// One recorded line. `seq` is assigned by the ring and only ever
 /// increases, so a reader that remembers where it got to can ask for what
 /// came after -- and a gap in the sequence is exactly the lines the bound
@@ -240,6 +249,35 @@ impl LogRing {
             .join("\n")
     }
 
+    /// The newest `max_lines` lines, formatted, with a first line naming
+    /// how many older ones were left out of *this* text when the ring held
+    /// more than that -- what `Copy report` appends instead of
+    /// [`Self::to_text`].
+    ///
+    /// Iris's own report: pasting the full ring (over a thousand lines on
+    /// a session that ran with tracing on) into a phone's message box was
+    /// what "causes a lot of lag" meant (docs/IRIS_TODO.md, 2026-09-07
+    /// night) -- nothing is actually lost, since `devlog`'s provider still
+    /// hands Dev Updater's Runtime tab the whole ring; this only caps what
+    /// gets inlined into a share.
+    pub fn tail_text(&self, max_lines: usize) -> String {
+        let lines = self.snapshot();
+        if lines.len() <= max_lines {
+            return lines
+                .iter()
+                .map(LogLine::format)
+                .collect::<Vec<_>>()
+                .join("\n");
+        }
+        let omitted = lines.len() - max_lines;
+        let tail = lines[lines.len() - max_lines..]
+            .iter()
+            .map(LogLine::format)
+            .collect::<Vec<_>>()
+            .join("\n");
+        format!("{omitted} earlier lines omitted; full log in Dev Updater's Runtime tab\n{tail}")
+    }
+
     /// One line for a diagnostics pane: how much is held, how much was
     /// dropped, and when the last line arrived. "no lines yet" is its own
     /// wording rather than a count of zero with a made-up time, because
@@ -270,6 +308,37 @@ impl LogRing {
     }
 }
 
+/// Whether a target belongs to this app's own crates (`iris` or
+/// `client_core`) rather than a dependency's -- `starts_with` guarded by an
+/// exact match or a `::` so an unrelated crate that merely begins with the
+/// same letters (there is no such crate today, but the check should not
+/// rely on that) is never mistaken for one of ours.
+fn is_own_target(target: &str) -> bool {
+    target == "iris"
+        || target.starts_with("iris::")
+        || target == "client_core"
+        || target.starts_with("client_core::")
+}
+
+/// Whether a line at `level` from `target` belongs in the ring, given
+/// whether tracing is on right now.
+///
+/// This is the one filter docs/IRIS_TODO.md's "logs way too big" entry
+/// asked for, applied once here rather than at each `debug!` call site:
+/// Info and above always ring, from anything, because a real warning or
+/// error from a dependency is worth keeping. Debug and Trace ring only
+/// from this app's own targets, and only while tracing is switched on --
+/// otherwise `naga::front`/`wgpu_core`/`jni` log at Debug unconditionally
+/// (the process logger's own level, set once at install and unrelated to
+/// tracing), which is what filled the ring with 1339 lines of it and
+/// dropped 4050 more before this existed. `iris`'s own Debug lines already
+/// self-gate on `iris::diagnostics::trace_enabled` at their call sites
+/// (commit 992c472); this is the backstop for lines this crate does not
+/// control.
+fn ring_accepts(level: log::Level, target: &str, trace_enabled: bool) -> bool {
+    level <= log::Level::Info || (trace_enabled && is_own_target(target))
+}
+
 /// A `log` backend that records into a [`LogRing`] **and** forwards to the
 /// logger the platform already installs, so nothing that reads the
 /// platform's log (`logcat`, a terminal) changes.
@@ -281,25 +350,40 @@ impl LogRing {
 pub struct RingLogger {
     ring: LogRing,
     inner: Box<dyn log::Log>,
+    /// Whether `iris::input`/`iris::frame`-style tracing is switched on
+    /// right now, consulted by [`ring_accepts`]. A plain fn pointer rather
+    /// than a dependency on `iris::diagnostics::trace_enabled` directly:
+    /// `client-core` sits below `iris` (AGENTS.md's "dependencies flow one
+    /// direction"), so the platform crate that depends on both is the one
+    /// that wires this closure through, the same way it already supplies
+    /// `inner`.
+    trace_enabled: fn() -> bool,
 }
 
 impl RingLogger {
-    pub fn new(ring: LogRing, inner: Box<dyn log::Log>) -> Self {
-        Self { ring, inner }
+    pub fn new(ring: LogRing, inner: Box<dyn log::Log>, trace_enabled: fn() -> bool) -> Self {
+        Self {
+            ring,
+            inner,
+            trace_enabled,
+        }
     }
 }
 
 impl log::Log for RingLogger {
     /// True for anything `log`'s own max level lets through: the ring
-    /// wants everything, even where the platform logger would filter it
-    /// out. The filter is applied per-logger in [`Self::log`] instead.
+    /// wants everything the *inner* logger might also want, even where the
+    /// platform logger would filter it out. Which lines the ring itself
+    /// keeps is decided in [`Self::log`] by [`ring_accepts`].
     fn enabled(&self, _metadata: &log::Metadata) -> bool {
         true
     }
 
     fn log(&self, record: &log::Record) {
+        if ring_accepts(record.level(), record.target(), (self.trace_enabled)()) {
             self.ring
                 .push(record.level(), record.target(), record.args().to_string());
+        }
         if self.inner.enabled(record.metadata()) {
             self.inner.log(record);
         }
@@ -320,8 +404,9 @@ pub fn install(
     ring: LogRing,
     inner: Box<dyn log::Log>,
     max_level: log::LevelFilter,
+    trace_enabled: fn() -> bool,
 ) -> Result<(), log::SetLoggerError> {
-    log::set_boxed_logger(Box::new(RingLogger::new(ring, inner)))?;
+    log::set_boxed_logger(Box::new(RingLogger::new(ring, inner, trace_enabled)))?;
     log::set_max_level(max_level);
     Ok(())
 }
@@ -349,12 +434,16 @@ pub fn process_ring() -> &'static LogRing {
 /// Installs [`process_ring`] as the recording half of the process logger,
 /// forwarding to `inner` (the platform's own logger, already configured).
 /// The platform half of AGENTS.md's sharing rule is `inner`; everything
-/// else is shared.
+/// else is shared. `trace_enabled` is the platform's own trace toggle
+/// (`iris::diagnostics::trace_enabled` on Android) -- see
+/// [`ring_accepts`] and the field doc on `RingLogger` for why it is
+/// passed in rather than called directly.
 pub fn install_process_logger(
     inner: Box<dyn log::Log>,
     max_level: log::LevelFilter,
+    trace_enabled: fn() -> bool,
 ) -> Result<(), log::SetLoggerError> {
-    install(process_ring().clone(), inner, max_level)
+    install(process_ring().clone(), inner, max_level, trace_enabled)
 }
 
 #[cfg(test)]
@@ -471,6 +560,33 @@ mod tests {
         assert_eq!(ring.to_text().lines().count(), 2);
     }
 
+    #[test]
+    fn tail_text_is_the_whole_ring_untouched_when_under_the_cap() {
+        let ring = LogRing::new(100, 1 << 20);
+        fill(&ring, 5);
+        assert_eq!(ring.tail_text(150), ring.to_text());
+    }
+
+    #[test]
+    fn tail_text_trims_to_the_newest_lines_and_says_how_many_were_left_out() {
+        let ring = LogRing::new(1000, 1 << 20);
+        fill(&ring, 200);
+        let tail = ring.tail_text(150);
+        let mut lines = tail.lines();
+        assert_eq!(
+            lines.next().unwrap(),
+            "50 earlier lines omitted; full log in Dev Updater's Runtime tab"
+        );
+        let rest: Vec<&str> = lines.collect();
+        assert_eq!(rest.len(), 150, "exactly the cap, after the header line");
+        assert!(
+            rest[0].ends_with("line 50"),
+            "the oldest line kept is the 50th, not line 0: {}",
+            rest[0]
+        );
+        assert!(rest.last().unwrap().ends_with("line 199"));
+    }
+
     #[test]
     fn an_empty_ring_says_so_rather_than_reporting_a_time() {
         let ring = LogRing::with_defaults();
@@ -522,19 +638,26 @@ mod tests {
 
         let seen = Arc::new(Mutex::new(Vec::new()));
         let ring = LogRing::with_defaults();
-        let logger = RingLogger::new(ring.clone(), Box::new(Collect(seen.clone(), Level::Info)));
+        // Own target, tracing on: this is the case where the ring and the
+        // inner logger disagree, which is the thing under test -- a
+        // foreign target is covered separately below.
+        let logger = RingLogger::new(
+            ring.clone(),
+            Box::new(Collect(seen.clone(), Level::Info)),
+            || true,
+        );
         logger.log(
             &log::Record::builder()
                 .args(format_args!("kept"))
                 .level(Level::Info)
-                .target("t")
+                .target("iris::test")
                 .build(),
         );
         logger.log(
             &log::Record::builder()
                 .args(format_args!("filtered"))
                 .level(Level::Debug)
-                .target("t")
+                .target("iris::test")
                 .build(),
         );
 
@@ -544,6 +667,91 @@ mod tests {
             "the inner logger's own filter still applies"
         );
         let held: Vec<String> = ring.snapshot().into_iter().map(|l| l.message).collect();
-        assert_eq!(held, ["kept", "filtered"], "the ring keeps both");
+        assert_eq!(
+            held,
+            ["kept", "filtered"],
+            "own-target debug still rings while tracing is on"
+        );
+    }
+
+    /// The bug this filter fixes: `naga`/`wgpu_core`/`jni` log at Debug
+    /// unconditionally, and used to flood the ring even though nothing in
+    /// this app asked for their Debug output. A foreign target's Debug
+    /// line must not ring even while tracing is on -- tracing controls
+    /// this app's own diagnostics, not a dependency's chatter.
+    #[test]
+    fn a_foreign_targets_debug_line_never_rings_even_while_tracing_is_on() {
+        use log::Log;
+        struct Discard;
+        impl Log for Discard {
+            fn enabled(&self, _: &log::Metadata) -> bool {
+                true
+            }
+            fn log(&self, _: &log::Record) {}
+            fn flush(&self) {}
+        }
+
+        let ring = LogRing::with_defaults();
+        let logger = RingLogger::new(ring.clone(), Box::new(Discard), || true);
+        logger.log(
+            &log::Record::builder()
+                .args(format_args!("naga debug spam"))
+                .level(Level::Debug)
+                .target("naga::front")
+                .build(),
+        );
+        logger.log(
+            &log::Record::builder()
+                .args(format_args!("naga warning"))
+                .level(Level::Warn)
+                .target("wgpu_core::device")
+                .build(),
+        );
+
+        let held: Vec<String> = ring.snapshot().into_iter().map(|l| l.message).collect();
+        assert_eq!(
+            held,
+            ["naga warning"],
+            "Info-and-above always rings; foreign Debug never does"
+        );
+    }
+
+    #[test]
+    fn ring_accepts_is_own_target_debug_only_while_tracing() {
+        assert!(
+            ring_accepts(Level::Info, "wgpu_core::device", false),
+            "Info+ from anything, tracing off"
+        );
+        assert!(
+            ring_accepts(Level::Warn, "jni", true),
+            "Info+ from anything, tracing on"
+        );
+        assert!(
+            !ring_accepts(Level::Debug, "jni", true),
+            "foreign Debug, tracing on: still excluded"
+        );
+        assert!(
+            !ring_accepts(Level::Debug, "iris::sense", false),
+            "own Debug, tracing off: excluded"
+        );
+        assert!(
+            ring_accepts(Level::Debug, "iris::sense", true),
+            "own Debug, tracing on: included"
+        );
+        assert!(
+            ring_accepts(Level::Trace, "client_core::api", true),
+            "own Trace, tracing on: included"
+        );
+    }
+
+    #[test]
+    fn is_own_target_matches_the_crate_or_its_modules_only() {
+        assert!(is_own_target("iris"));
+        assert!(is_own_target("iris::sense"));
+        assert!(is_own_target("client_core"));
+        assert!(is_own_target("client_core::log_ring"));
+        assert!(!is_own_target("iris_something_else"));
+        assert!(!is_own_target("naga::front"));
+        assert!(!is_own_target("jni"));
     }
 }