base: Add structured logging rate limiter and thermald integration (P50)

Add RateLimitedLog to common::logger for per-message rate limiting with
"last message repeated N times" warnings. Add structured_log! macro for
key=value formatted logs. Update thermald to rate-limit the max-temp
summary line (30s interval) to reduce log volume.

local/patches/base/P50-structured-logging.patch

@@ -0,0 +1,93 @@
+diff --git a/drivers/common/src/lib.rs b/drivers/common/src/lib.rs
+index a55014b9..6b7ab2fe 100644
+--- a/drivers/common/src/lib.rs
++++ b/drivers/common/src/lib.rs
+@@ -25 +25 @@ pub mod timeout;
+-pub use logger::{file_level, output_level, setup_logging};
++pub use logger::{file_level, output_level, setup_logging, RateLimitedLog};
+diff --git a/drivers/common/src/logger.rs b/drivers/common/src/logger.rs
+index a531edd9..8b65f6bd 100644
+--- a/drivers/common/src/logger.rs
++++ b/drivers/common/src/logger.rs
+@@ -0,0 +1,2 @@
++use std::cell::RefCell;
++use std::collections::HashMap;
+@@ -71,0 +74,65 @@ pub fn setup_logging(
++/// A simple per-message rate limiter to prevent log spam.
++///
++/// Tracks the last emission time for each unique message key. If the same
++/// key is logged again within `interval`, the message is suppressed and a
++/// "last message repeated N times" warning is emitted instead.
++pub struct RateLimitedLog {
++    interval: std::time::Duration,
++    last_emission: RefCell<HashMap<String, std::time::Instant>>,
++    suppress_count: RefCell<HashMap<String, u64>>,
++}
++
++impl RateLimitedLog {
++    pub fn new(interval_secs: u64) -> Self {
++        Self {
++            interval: std::time::Duration::from_secs(interval_secs),
++            last_emission: RefCell::new(HashMap::new()),
++            suppress_count: RefCell::new(HashMap::new()),
++        }
++    }
++
++    /// Log a message through the rate limiter.
++    pub fn log(&self, key: &str, log_fn: impl FnOnce()) {
++        let now = std::time::Instant::now();
++        let mut last_map = self.last_emission.borrow_mut();
++        let mut count_map = self.suppress_count.borrow_mut();
++
++        if let Some(last) = last_map.get(key) {
++            if now.duration_since(*last) < self.interval {
++                *count_map.entry(key.to_string()).or_insert(0) += 1;
++                return;
++            }
++        }
++
++        if let Some(count) = count_map.remove(key) {
++            if count > 0 {
++                log::warn!("RateLimitedLog: last message '{}' repeated {} times", key, count);
++            }
++        }
++
++        last_map.insert(key.to_string(), now);
++        log_fn();
++    }
++}
++
++/// Format a structured log message with key=value pairs.
++///
++/// Example: `structured_log!("thermald", "event=temperature_read", "zone=CPU", "temp=45.2")`
++/// produces: `thermald: event=temperature_read zone=CPU temp=45.2`
++#[macro_export]
++macro_rules! structured_log {
++    ($source:expr, $($key:expr),+ $(,)?) => {
++        {
++            let mut msg = String::new();
++            msg.push_str($source);
++            msg.push_str(": ");
++            $(
++                msg.push_str($key);
++                msg.push(' ');
++            )+
++            msg.pop();
++            log::info!("{}", msg);
++        }
++    };
++}
++
+diff --git a/drivers/thermald/src/main.rs b/drivers/thermald/src/main.rs
+index b8d271b5..e64cf162 100644
+--- a/drivers/thermald/src/main.rs
++++ b/drivers/thermald/src/main.rs
+@@ -86,0 +87,2 @@ fn main() -> Result<()> {
++    let rate_limiter = common::RateLimitedLog::new(30);
++
+@@ -138 +140,4 @@ fn main() -> Result<()> {
+-            log::info!("thermald: max temp = {:.1}C from {}", max_temp, max_source);
++            let source = max_source.clone();
++            rate_limiter.log(&format!("max_temp_{:.0}", max_temp), || {
++                log::info!("thermald: max temp = {:.1}C from {}", max_temp, source);
++            });

recipes/core/base/recipe.toml

@@ -99,6 +99,8 @@ patches = [
     "P48-acpid-fan-support.patch",
     # P49: Add IRQ affinity logging and CPU tracking to pcid
     "P49-irq-affinity-logging.patch",
+    # P50: Add structured logging rate limiter and thermald integration
+    "P50-structured-logging.patch",
 ]
 
 [package]