From a1d1e721b6df0ee7f0c0dfd3a552351fb5f90630 Mon Sep 17 00:00:00 2001
From: John Alanbrook <john@pockle.world>
Date: Wed, 18 Feb 2026 12:22:33 -0600
Subject: [PATCH] stack trace in logging toml

---
 docs/logging.md    | 17 +++++++++--------
 internal/engine.cm | 25 ++++++++++++++++++++-----
 2 files changed, 29 insertions(+), 13 deletions(-)

diff --git a/docs/logging.md b/docs/logging.md
index 3d4e8ec9..2aea9e42 100644
--- a/docs/logging.md
+++ b/docs/logging.md
@@ -68,6 +68,7 @@ exclude = ["console"]
 | `format` | `"pretty"`, `"bare"`, `"json"` | How output is formatted |
 | `channels` | array of names, or `["*"]` | Which channels this sink receives. Quote `'*'` on the CLI to prevent shell glob expansion. |
 | `exclude` | array of names | Channels to skip (useful with `"*"`) |
+| `stack` | array of channel names | Channels that capture a stack trace |
 | `path` | file path | Output file (file sinks only) |
 
 ### Formats
@@ -113,33 +114,33 @@ File sinks write one JSON-encoded record per line. Console sinks format the reco
 
 ## Stack Traces
 
-Set `stack = true` at the top level of `.cell/log.toml` to capture a full call stack with every log record.
+Add a `stack` field to a sink to capture a full call stack for specific channels. The value is an array of channel names.
 
 ```toml
-stack = true
-
 [sink.terminal]
 type = "console"
-format = "pretty"
+format = "bare"
 channels = ["console", "error"]
+stack = ["error"]
 ```
 
-With pretty format, the stack is printed indented below each message:
+Only channels listed in `stack` get stack traces. Other channels on the same sink print without one:
 
 ```
-[a3f12] [error] server.ce:42 connection failed
+[a3f12] server started
+[a3f12] connection failed
     at handle_request (server.ce:42:3)
     at process (router.ce:18:5)
     at main (main.ce:5:1)
 ```
 
-With JSON format, a `stack` array is added to the record:
+With JSON format, a `stack` array is added to the record for channels that have stack capture enabled:
 
 ```json
 {"actor_id":"a3f12...","channel":"error","event":"connection failed","source":{"file":"server.ce","line":42,"col":3,"fn":"handle_request"},"stack":[{"fn":"handle_request","file":"server.ce","line":42,"col":3},{"fn":"process","file":"router.ce","line":18,"col":5},{"fn":"main","file":"main.ce","line":5,"col":1}]}
 ```
 
-When `stack` is not set or `false`, no stack is captured and the `stack` field is omitted from records. Capturing stacks adds overhead — enable it for debugging, not production.
+Channels without `stack` configuration produce no stack field. Capturing stacks adds overhead — enable it for debugging, not production.
 
 ## CLI
 
diff --git a/internal/engine.cm b/internal/engine.cm
index 2ef5b826..8dcf5792 100644
--- a/internal/engine.cm
+++ b/internal/engine.cm
@@ -324,7 +324,7 @@ var log_config = null
 var channel_sinks = {}
 var wildcard_sinks = []
 var warned_channels = {}
-var log_stack_enabled = false
+var stack_channels = {}
 
 function log(name, args) {
   var msg = args[0]
@@ -438,6 +438,7 @@ function ensure_log_dir(path) {
 function build_sink_routing() {
   channel_sinks = {}
   wildcard_sinks = []
+  stack_channels = {}
   var names = array(log_config.sink)
   arrfor(names, function(name) {
     var sink = log_config.sink[name]
@@ -445,7 +446,12 @@ function build_sink_routing() {
     if (!is_array(sink.channels)) sink.channels = []
     if (is_text(sink.exclude)) sink.exclude = [sink.exclude]
     if (!is_array(sink.exclude)) sink.exclude = []
+    if (is_text(sink.stack)) sink.stack = [sink.stack]
+    if (!is_array(sink.stack)) sink.stack = []
     if (sink.type == "file" && sink.path) ensure_log_dir(sink.path)
+    arrfor(sink.stack, function(ch) {
+      stack_channels[ch] = true
+    })
     arrfor(sink.channels, function(ch) {
       if (ch == "*") {
         wildcard_sinks[] = sink
@@ -471,13 +477,13 @@ function load_log_config() {
         terminal: {
           type: "console",
           format: "pretty",
-          channels: ["console", "error", "system"]
+          channels: ["console", "error", "system"],
+          stack: ["error"]
         }
       }
     }
   }
   build_sink_routing()
-  log_stack_enabled = log_config.stack == true
 }
 
 function pretty_format(rec) {
@@ -503,7 +509,16 @@ function pretty_format(rec) {
 function bare_format(rec) {
   var aid = text(rec.actor_id, 0, 5)
   var ev = is_text(rec.event) ? rec.event : json.encode(rec.event, false)
-  return `[${aid}] ${ev}\n`
+  var out = `[${aid}] ${ev}\n`
+  var i = 0
+  var fr = null
+  if (rec.stack && length(rec.stack) > 0) {
+    for (i = 0; i < length(rec.stack); i = i + 1) {
+      fr = rec.stack[i]
+      out = out + `    at ${fr.fn} (${fr.file}:${text(fr.line)}:${text(fr.col)})\n`
+    }
+  }
+  return out
 }
 
 function sink_excluded(sink, channel) {
@@ -549,7 +564,7 @@ log = function(name, args) {
   }
 
   caller = caller_info(2)
-  if (log_stack_enabled) stack = os.stack(1)
+  if (stack_channels[name]) stack = os.stack(1)
   rec = {
     actor_id: _cell.id,
     timestamp: time.number(),