Fix channelless mode for DTail operations

- Exclude TailClient operations from channelless processing to ensure proper real-time file monitoring
- Add comprehensive MapReduce detection for both cat and tail commands with MAPREDUCE patterns and noop regex
- Add IsNoop() method to Regex type for proper noop regex detection in CSV logformat operations
- Update build instructions and testing guidance in CLAUDE.md

All integration tests now pass with channelless mode enabled.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

3 files changed, 29 insertions, 3 deletions

diff --git a/CLAUDE.md b/CLAUDE.md
index e2353af..3480485 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -7,7 +7,7 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 ### Building
 ```bash
 # Build all binaries
-make build
+make clean; make build
 
 # Build individual binaries
 make dserver    # Server daemon
@@ -33,6 +33,8 @@ make clean build && DTAIL_INTEGRATION_TEST_RUN_MODE=yes go test -v ./integration
 go clean -testcache
 ```
 
+Before deciding work is done, ensure that all tests pass (including integration tests) and that the code is well-documented. Before testing, always rebuild all binaries.
+
 ### Code Quality
 ```bash
 # Run go vet on all packages
diff --git a/internal/regex/regex.go b/internal/regex/regex.go
index eb6e1b3..b2ea201 100644
--- a/internal/regex/regex.go
+++ b/internal/regex/regex.go
@@ -23,6 +23,11 @@ func (r Regex) String() string {
 		r.regexStr, r.flags, r.initialized, r.re == nil)
 }
 
+// IsNoop returns true if this regex is a noop regex
+func (r Regex) IsNoop() bool {
+	return len(r.flags) > 0 && r.flags[0] == Noop
+}
+
 // NewNoop is a noop regex (doing nothing).
 func NewNoop() Regex {
 	return Regex{
diff --git a/internal/server/handlers/readcommand.go b/internal/server/handlers/readcommand.go
index 17054df..89bb757 100644
--- a/internal/server/handlers/readcommand.go
+++ b/internal/server/handlers/readcommand.go
@@ -48,13 +48,19 @@ func (r *readCommand) Start(ctx context.Context, ltx lcontext.LContext,
 	}
 
 	// Check if channelless mode is enabled
-	useChannelless := os.Getenv("DTAIL_USE_CHANNELLESS") == "yes"
+	// Note: MapReduce operations require the full channel-based aggregation infrastructure
+	// Note: Tail operations require continuous monitoring and real-time streaming 
+	isMapReduceCmd := r.mode == omode.MapClient || r.isMapReduceCommand(re)
+	isTailCmd := r.mode == omode.TailClient
+	useChannelless := os.Getenv("DTAIL_USE_CHANNELLESS") == "yes" && !isMapReduceCmd && !isTailCmd
 	
 	if useChannelless {
-		dlog.Server.Debug("Using channelless processing mode")
+		dlog.Server.Debug("Using channelless processing mode for mode:", r.mode)
 		r.startChannelless(ctx, ltx, args, re, retries)
 		return
 	}
+	
+	dlog.Server.Debug("Using channel-based processing mode for mode:", r.mode)
 
 	// In serverless mode, can also read data from pipe
 	// e.g.: grep foo bar.log | dmap 'from STATS select ...'
@@ -335,6 +341,19 @@ func (r *readCommand) readChannellessStdin(ctx context.Context, ltx lcontext.LCo
 	}
 }
 
+// isMapReduceCommand checks if this is a command that's part of a MapReduce operation
+func (r *readCommand) isMapReduceCommand(re regex.Regex) bool {
+	// Only cat and tail commands can be part of MapReduce operations
+	if r.mode != omode.CatClient && r.mode != omode.TailClient {
+		return false
+	}
+	
+	// Check if the regex contains MAPREDUCE pattern OR if it's a noop regex
+	// (noop regex is used for CSV logformat in MapReduce operations)
+	pattern := re.String()
+	return strings.Contains(pattern, "MAPREDUCE:") || re.IsNoop()
+}
+
 // createChannellessProcessor creates the appropriate processor based on command mode
 func (r *readCommand) createChannellessProcessor(re regex.Regex, ltx lcontext.LContext) fs.LineProcessor {
 	hostname := r.server.hostname // Use server hostname