Causality is an interface.

slos:/$ events 8
  ID    TICK    TYPE        DESCRIPTION
  4215  18394   sched       switch pid=12 -> pid=31
  4216  18396   shell       command: note add field report
  4217  18397   syscall     write pid=31
  4218  18397   fs          write /notes.db
  4219  18398   user        notes event appended
  4220  18399   syscall     yield pid=31

slos:/$ why 4219
Causal chain for event 4219:

[4219] T+183.98s notes: notes event appended
  └─ [4218] T+183.97s fs: write /notes.db
     └─ [4217] T+183.97s syscall: write pid=31
        └─ [4216] T+183.96s shell: command: note add field report

slos:/$ trace 4219
  [4219] t=18398 notes: notes event appended
    └─ caused by:
  [4218] t=18397 fs: write /notes.db
    └─ caused by:
  [4217] t=18397 syscall: write pid=31
    └─ caused by:
  [4216] t=18396 shell: command: note add field report

slos:/$ blast 4216
Forward trace from event #4216:
  [4217] T+18397 syscall: write pid=31
  [4218] T+18397 fs: write /notes.db
  [4219] T+18398 notes: notes event appended

slos:/$ cpath 4216 4219
Causal path #4216 -> #4219:
  [4216] T+18396 shell: command: note add field report
  [4217] T+18397 syscall: write pid=31
  [4218] T+18397 fs: write /notes.db
  [4219] T+18398 notes: notes event appended
cpath: 3 hops
slos:/$ cpath common 4219 4220
Nearest common ancestor of #4219 and #4220: #4216
  [4216] T+18396 shell: command: note add field report
cpath: dist 3 from #4219, 1 from #4220

slos:/$ journal
Causal Journal:
  Status:     active
  Segments:   24 / 32 max
  Persisted:  12288 events
  ID range:   1 -- 12288 (on disk) | 12289 -- 16384 (in ring)
  Ring:       4096 / 16384

slos:/$ journal find notes 5
Journal find "notes": 5 events
  #3182  T+14211 hash=0x8b7a12f0 hashv=4 source=journal transport=syscall fs blockfs write /notes.db

slos:/$ events -a subsystem fs 5
Journal subsystem fs: 5 events

slos:/$ scrub 18400
SlOS Causal Time-Travel  tick 18400 / 18402
[=======================================-]
Reconstructed state (replay of 4218 events):
  tasks: alive 9  created 31  exited 22
  io:    syscalls 701  fs 211  net tx/rx 44/88  actor msgs 37
Active tasks (9):
  [pid 31] shell
Recent events (8): #4215 #4216 #4217 #4218 #4219 #4220 #4221 #4222

slos:/$ scrub event 4219
Event #4219 focus
  type=USER subsystem=notes tick=T+18398
  origin: node=0x4f2a19d0 (local)
  desc: notes event appended
Caused by (parents):
  #4218 fs: write /notes.db
  #4217 syscall: write pid=31
  #4216 shell: command: note add field report
Led to (effects):
  #4220 syscall: yield pid=31

slos:/$ scrub diff 18000 18400
Causal diff: tick 18000 -> tick 18400
  events +41   syscalls +2   fs +3
  net tx +0   net rx +0   actor +1
  tasks alive: 8 -> 9

slos:/$ httpd
[httpd] Started (pid 18) — http://10.0.2.15/ (host: http://localhost:8080/)
[httpd] Listening on port 80 — dashboard at http://<ip>/

host:$ curl http://10.0.2.15/api/causal/state
{"tick":18402,"total_events":4222,"tasks":{"alive":9,"created":31,"exited":22},"io":{"syscalls":703,"fs":214,"net_tx":44,"net_rx":88,"actor_msgs":37},"active_tasks":[{"pid":31,"name":"shell"}],"recent_events":[4217,4218,4219,4220,4221,4222]}

host:$ curl http://10.0.2.15/api/causal/state?tick=18000
{"tick":18000,"total_events":4181,"tasks":{"alive":8,"created":30,"exited":22},"io":{"syscalls":690,"fs":208,"net_tx":44,"net_rx":88,"actor_msgs":36},"active_tasks":[{"pid":31,"name":"shell"}],"recent_events":[4176,4177,4178,4179,4180,4181]}

host:$ curl http://10.0.2.15/api/causal/dot
digraph causal {
  "4216" -> "4217";
}

host:$ curl http://10.0.2.15/api/causal/graph
{"nodes":[{"id":4216,"tick":18396,"type":"shell","subsystem":"shell","desc":"command: note add field report","remote":false}],"edges":[{"from":4216,"to":4217}]}

slos:/$ ctop 128
ctop - causal activity by subsystem (last 128 events)
  SUBSYSTEM     EVENTS  SHARE
  syscall          42    32% ########
  fs               31    24% ######
  sched            25    19% ####

slos:/$ lens save fsnotes cq -a type=fs desc~notes limit=8
lens: saved 'fsnotes' = cq -a type=fs desc~notes limit=8
slos:/$ lens fsnotes
Journal filter: 8 events

slos:/$ journal type sched 50 | tally
sched.switch  31
sched.wake    12
sched.exit     7

slos:/$ why --md last
# Why event 4222

Causal chain (most recent first):

- **[4222]** T+184.02s `syscall`: write pid=31
  - **[4219]** T+183.98s `notes`: notes event appended
    - **[4218]** T+183.97s `fs`: write /notes.db

_Root cause reached._

slos:/$ triage
SYSTEM TRIAGE  (tick 281)
====================================
STATUS: HEALTHY

Findings:
  [INFO] journal: durable; 0 event(s) in 0 segment(s) (verify journal for deep check)
  [ OK ] no anomalies, faults, or contract violations

Next action: (system healthy - no action needed)

slos:/$ cbisect events 100
CAUSAL BISECT: earliest tick where events >= 100
  range [0 .. 282], reconstructing state per probe via replay
  probe tick 141 -> events=0  miss
  probe tick 276 -> events=2049  hit
  probe tick 275 -> events=0  miss
FOUND: tick 276 (events=2049, crossed from 0) after 8 probes
  Next: replay at 276   (full reconstructed state)   |   events   (browse history)