Diagnostics and debugging

SessionReport

SessionReport captures structured diagnostics:

• pipeline string (for reproduction)
• canonical error_code (machine triage)
• repro_note (human summary + hint)
• node reports and owned element names
• bus messages and error details
• optional flow/timing counters

When an error occurs, SessionError carries a SessionReport you can log or serialize.

Error taxonomy

Framework errors use stable code families:

Error code	Meaning	Typical fix
misconfig.pipeline_shape	Node order/shape contract violation	Ensure Input() first for push pipelines and Output() last for pull pipelines
misconfig.caps	Caps negotiation/override mismatch	Align caps_override, format, and downstream caps
misconfig.input_shape	Input tensor/frame/sample shape/layout mismatch	Validate width/height/depth, layout, dtype, storage
build.parse_launch	gst_parse_launch failed	Validate fragment syntax and plugin availability
runtime.pull	Runtime pull/timeout/closed-output failure	Check sink output production, queue pressure, and upstream errors
io.parse	Saved-session JSON parse/schema failure	Validate JSON and required node fields
io.open	Session save/load file open/read/write failure	Check path existence, permissions, and storage health

PullError.code uses the same taxonomy (not only exception paths).

Programmatic handling

#include "pipeline/ErrorCodes.h"
#include "pipeline/SessionError.h"

try {
  auto run = session.build(input);
  simaai::neat::Sample out;
  simaai::neat::PullError perr;
  const auto st = run.pull(500, out, &perr);
  if (st == simaai::neat::PullStatus::Error &&
      perr.code == simaai::neat::error_codes::kRuntimePull) {
    // runtime pull triage path
  }
} catch (const simaai::neat::SessionError& e) {
  if (e.report().error_code == simaai::neat::error_codes::kParseLaunch) {
    // build/parse-launch triage path
  }
}

Debug knobs (environment)

Key environment variables (see Architecture for detail):

• SIMA_GST_DOT_DIR: write DOT graphs for failures
• SIMA_GST_BOUNDARY_PROBES: boundary flow counters
• SIMA_GST_ELEMENT_TIMINGS: per-element timings
• SIMA_GST_FLOW_DEBUG: per-element flow counters
• SIMA_GST_ENFORCE_NAMES: enforce naming contract

Debug workflow

1. Capture SessionReport.error_code and bucket the failure by taxonomy first.
2. Capture SessionReport.repro_note for concrete context and built-in hint.
3. Capture pipeline text: Session::describe_backend() or last_pipeline().
4. Capture structured diagnostics: Run::report() or SessionError::report().
5. Inspect SessionReport.bus for first terminal ERROR source + detail.
6. If runtime stalls/timeouts, enable boundary/element probes to localize flow stop.

Recommended support bundle:

• error_code
• repro_note
• full pipeline_string
• first 3-5 terminal bus errors (SessionReport.bus)
• environment overrides used in run/validate

Common failures → fixes

Symptom	Likely cause	Fix
missing ... plugin	GStreamer plugin not found	Check GST_PLUGIN_PATH, run gst-inspect-1.0 <plugin>
appsink 'mysink' not found	Missing terminal Output()	Ensure Output is the last node in run/build pipelines
caps_override is set; renegotiation disabled	caps pinned	Remove caps_override or keep input caps fixed
tensor caps change not supported	Tensor shape/dtype change at runtime	Keep tensor shape/dtype stable (no renegotiation)

For structured plugin errors and actionable hints, see How To Debug Plugin Failures.