fix(923): watchdog counts only tool-using turns; narration-only turns no longer burn budget

Observed: stories 917, 918, 920, 910 all turn-limit-killed despite producing
real commits. Tally across their session logs shows 30–55% of assistant
turns were pure narration ("I'll read X next", "Now let me check Y") with
no tool_use. At 80 max_turns the effective work budget was ~44 tool calls,
not enough for a typical bug fix's edit + test + check_criterion cycle.

Changes:
- New optional AgentConfig field max_tool_turns. When set the watchdog
  uses it instead of max_turns; only assistant messages whose
  data.message.content has at least one tool_use block count.
- count_turns_in_log in agents/pool/auto_assign/watchdog/limits.rs
  filters on tool_use. Existing test helper write_fake_session_log now
  emits tool_use blocks; added write_fake_mixed_session_log for the
  narration regression test.
- agents.toml: coders/coder-opus get max_turns=200 (claude-code's own
  --max-turns cap, sized to never bite before the watchdog) and
  max_tool_turns=80. qa: 120 / 40. mergemaster: 250 / 100. Budgets
  unchanged — the dollar cap remains the runaway-loop backstop, with
  ~$3-5 worst-case waste if an agent narrates indefinitely.
- Two new regression tests:
  * watchdog_does_not_count_narration_only_turns: 5 tool + 30 narration
    under max_tool_turns=10 stays Running.
  * watchdog_max_tool_turns_overrides_max_turns: 4 tool turns at
    max_tool_turns=3 / max_turns=200 still terminates with TurnLimit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/src/agents/pool/auto_assign/watchdog/limits.rs

@@ -41,7 +41,13 @@ pub(crate) fn resolve_session_log(
     crate::agent_log::find_latest_log(project_root, story_id, agent_name)
 }
 
-/// Count `assistant` events in a single log file.
+/// Count **tool-using** assistant turns in a single log file (story 923).
+///
+/// A turn counts only if its assistant message contains at least one
+/// `content` block with `type == "tool_use"`. Narration-only turns
+/// (text-only assistant messages such as "I'll read X next" preambles)
+/// don't count against the watchdog limit — they make no progress, only
+/// burn budget, and Sonnet emits them at roughly 30–55% of all turns.
 pub(crate) fn count_turns_in_log(path: &Path) -> u64 {
     let entries = match crate::agent_log::read_log(path) {
         Ok(e) => e,
@@ -50,13 +56,24 @@ pub(crate) fn count_turns_in_log(path: &Path) -> u64 {
     entries
         .iter()
         .filter(|entry| {
-            entry.event.get("type").and_then(|v| v.as_str()) == Some("agent_json")
-                && entry
-                    .event
-                    .get("data")
-                    .and_then(|d| d.get("type"))
-                    .and_then(|v| v.as_str())
-                    == Some("assistant")
+            if entry.event.get("type").and_then(|v| v.as_str()) != Some("agent_json") {
+                return false;
+            }
+            let data = match entry.event.get("data") {
+                Some(d) => d,
+                None => return false,
+            };
+            if data.get("type").and_then(|v| v.as_str()) != Some("assistant") {
+                return false;
+            }
+            // Require at least one tool_use content block.
+            data.pointer("/message/content")
+                .and_then(|c| c.as_array())
+                .map(|arr| {
+                    arr.iter()
+                        .any(|item| item.get("type").and_then(|v| v.as_str()) == Some("tool_use"))
+                })
+                .unwrap_or(false)
         })
         .count() as u64
 }
@@ -103,7 +120,10 @@ pub(super) fn check_agent_limits(
 
     for (key, story_id, agent_name, tx, log_session_id) in &running {
         let agent_config = config.agent.iter().find(|a| a.name == *agent_name);
-        let max_turns = agent_config.and_then(|a| a.max_turns);
+        // The watchdog gates on max_tool_turns (counts only tool-using
+        // assistant turns) when set; otherwise falls back to max_turns for
+        // backwards compatibility with configs that haven't migrated yet.
+        let max_turns = agent_config.and_then(|a| a.max_tool_turns.or(a.max_turns));
         let max_budget_usd = agent_config.and_then(|a| a.max_budget_usd);
 
         // Skip agents with no limits configured.