feat: complete OTEL tracing across all services with pipeline bridge and docs

Extends tracing to every remaining module: all 23 API route handlers,
correlation engine, sniffer (fingerprint/p0f/syslog), prober (jarm/hassh/tcpfp),
profiler behavioral analysis, logging subsystem, engine, and mutator.

Bridges the ingester→SSE trace gap by persisting trace_id/span_id columns on
the logs table and creating OTEL span links in the SSE endpoint. Adds log-trace
correlation via _TraceContextFilter injecting otel_trace_id into Python LogRecords.

Includes development/docs/TRACING.md with full span reference (76 spans),
pipeline propagation architecture, quick start guide, and troubleshooting.

decnet/logging/__init__.py

@@ -7,6 +7,11 @@ Usage:
 
 The returned logger propagates to the root logger (configured in config.py with
 Rfc5424Formatter), so level control via DECNET_DEVELOPER still applies globally.
+
+When ``DECNET_DEVELOPER_TRACING`` is active, every LogRecord is enriched with
+``otel_trace_id`` and ``otel_span_id`` from the current OTEL span context.
+This lets you correlate log lines with Jaeger traces — click a log entry and
+jump straight to the span that produced it.
 """
 
 from __future__ import annotations
@@ -27,6 +32,51 @@ class _ComponentFilter(logging.Filter):
         return True
 
 
+class _TraceContextFilter(logging.Filter):
+    """Injects ``otel_trace_id`` and ``otel_span_id`` onto every LogRecord
+    from the active OTEL span context.
+
+    Installed once by ``enable_trace_context()`` on the root ``decnet`` logger
+    so all child loggers inherit the enrichment via propagation.
+
+    When no span is active, both fields are set to ``"0"`` (cheap string
+    comparison downstream, no None-checks needed).
+    """
+
+    def filter(self, record: logging.LogRecord) -> bool:
+        try:
+            from opentelemetry import trace
+            span = trace.get_current_span()
+            ctx = span.get_span_context()
+            if ctx and ctx.trace_id:
+                record.otel_trace_id = format(ctx.trace_id, "032x")  # type: ignore[attr-defined]
+                record.otel_span_id = format(ctx.span_id, "016x")  # type: ignore[attr-defined]
+            else:
+                record.otel_trace_id = "0"  # type: ignore[attr-defined]
+                record.otel_span_id = "0"  # type: ignore[attr-defined]
+        except Exception:
+            record.otel_trace_id = "0"  # type: ignore[attr-defined]
+            record.otel_span_id = "0"  # type: ignore[attr-defined]
+        return True
+
+
+_trace_filter_installed: bool = False
+
+
+def enable_trace_context() -> None:
+    """Install the OTEL trace-context filter on the root ``decnet`` logger.
+
+    Called once from ``decnet.telemetry.setup_tracing()`` after the
+    TracerProvider is initialised.  Safe to call multiple times (idempotent).
+    """
+    global _trace_filter_installed
+    if _trace_filter_installed:
+        return
+    root = logging.getLogger("decnet")
+    root.addFilter(_TraceContextFilter())
+    _trace_filter_installed = True
+
+
 def get_logger(component: str) -> logging.Logger:
     """Return a named logger that self-identifies as *component* in RFC 5424.
 

decnet/logging/file_handler.py

@@ -13,6 +13,8 @@ import logging.handlers
 import os
 from pathlib import Path
 
+from decnet.telemetry import traced as _traced
+
 _LOG_FILE_ENV = "DECNET_LOG_FILE"
 _DEFAULT_LOG_FILE = "/var/log/decnet/decnet.log"
 _MAX_BYTES = 10 * 1024 * 1024  # 10 MB
@@ -22,10 +24,10 @@ _handler: logging.handlers.RotatingFileHandler | None = None
 _logger: logging.Logger | None = None
 
 
-def _get_logger() -> logging.Logger:
+@_traced("logging.init_file_handler")
+def _init_file_handler() -> logging.Logger:
+    """One-time initialisation of the rotating file handler."""
     global _handler, _logger
-    if _logger is not None:
-        return _logger
 
     log_path = Path(os.environ.get(_LOG_FILE_ENV, _DEFAULT_LOG_FILE))
     log_path.parent.mkdir(parents=True, exist_ok=True)
@@ -46,6 +48,12 @@ def _get_logger() -> logging.Logger:
     return _logger
 
 
+def _get_logger() -> logging.Logger:
+    if _logger is not None:
+        return _logger
+    return _init_file_handler()
+
+
 def write_syslog(line: str) -> None:
     """Write a single RFC 5424 syslog line to the rotating log file."""
     try:

decnet/logging/forwarder.py

@@ -11,6 +11,8 @@ shared utilities for validating and parsing the log_target string.
 
 import socket
 
+from decnet.telemetry import traced as _traced
+
 
 def parse_log_target(log_target: str) -> tuple[str, int]:
     """
@@ -23,6 +25,7 @@ def parse_log_target(log_target: str) -> tuple[str, int]:
     return parts[0], int(parts[1])
 
 
+@_traced("logging.probe_log_target")
 def probe_log_target(log_target: str, timeout: float = 2.0) -> bool:
     """
     Return True if the log target is reachable (TCP connect succeeds).