Tool runner: the cap's reason fails the call; the test proves the ending; the refused-answer limit keys on the caller's prefix and forgets old entries (issue 1966, review round 1)

Claude-Session: https://claude.ai/code/session_01NcbgfFfQ4Z9UE5jK32PmE5

node-tools/internal/launch/launch.go

@@ -206,6 +206,8 @@ type child struct {
 	// restart decided — which Stop waits for (novox/hq issue 476).
 	handled chan struct{}
 	why     error
+	// endedFor is why the runner itself ended the bundle (a line over the cap); its calls fail with it.
+	endedFor string
 	// watches are the state watches this child asked for, stopped when it exits (ADR 0201): a child
 	// that starts again watches again, as its code runs again.
 	watches []func()
@@ -351,8 +353,11 @@ func Start(module, entry string, env []string, mesh Bus, logf func(string, ...an
 					// Never left frozen (issue 1966): a reader that stops while the bundle lives leaves the bundle's
 					// next write blocked for good. Said, and the bundle ended; the exit path below fails what waits
 					// on it and starts it again.
-					logf("[mesh-tools] %s's bundle wrote a line over %d bytes (a tool's answer the bus cannot carry); ending the bundle",
-						module, maxLine)
+					reason := fmt.Sprintf("%s's bundle wrote a line over %d bytes (a tool's answer the bus cannot carry)", module, maxLine)
+					logf("[mesh-tools] %s; ending the bundle", reason)
+					c.mu.Lock()
+					c.endedFor = reason
+					c.mu.Unlock()
 					_ = cmd.Process.Kill()
 					break
 				}
@@ -561,6 +566,9 @@ func Start(module, entry string, env []string, mesh Bus, logf func(string, ...an
 			}
 			saidMu.Unlock()
 			c.mu.Lock()
+			if c.endedFor != "" {
+				why = c.endedFor + "; the bundle was ended (" + code + ")"
+			}
 			c.why = errors.New(why)
 			watches := c.watches
 			c.watches = nil