Add optional [LAT] latency-profiling log points

[Thecave3]

What

Compile-gated [LAT] log markers on the E3 send / receive / dispatch boundaries, so the end-to-end critical path can be measured offline from interleaved logs — no wire or schema change.

How

• New include/libe3/latency.hpp — E3_LAT / E3_LAT_CLOCK_OFFSET macros emitting one machine-parseable INFO line:

  [LAT] stage=<name> t_ns=<monotonic ns> anchor_ns=<producer_ts|0> [k=v ...]
  

  t_ns uses steady_clock (== CLOCK_MONOTONIC on glibc), so it subtracts directly against same-node C timestamps. When disabled the macros collapse to a dead NullLatSink chain (zero cost).
• New CMake option LIBE3_ENABLE_LATENCY (default OFF) → defines LIBE3_LATENCY on both library targets. Gating is the compile switch, not the log level — a profiling run does not have to raise the logger to DEBUG.
• src/core/e3_interface.cpp: ind_wire_tx (outbound send), ctrl_wire_rx (inbound control off the wire), ctrl_dispatch (handoff to the SM), plus a per-process clock_offset marker at inbound-loop start.

Enabling

./build_libe3 --install --cmake-opt "-DLIBE3_ENABLE_LATENCY=ON"

Testing

Default builds are unaffected (macros expand away). With the option on, [LAT] lines appear at INFO for each boundary plus one clock_offset line at startup.

[github-actions]

⏱️ Full-loop Latency Benchmark (commit a4c1818)

Full-loop latency benchmark (N=1038 after 50 warmup)

All values in microseconds (us). Link: zmq, transport: ipc, encoding: ASN.1 APER.

Phase	mean	p50	p99	max
1. Collect indication data	0.10	0.11	0.28	1.28
2. Create & encode indication	0.52	0.45	1.22	13.34
3. Deliver indication (RAN -> dApp)	81.48	75.28	142.93	153.04
4. Decode indication	0.31	0.25	0.94	8.73
5. Process data	0.02	0.02	0.03	0.13
6. Create & encode control	0.22	0.17	0.60	2.81
7. Deliver control (dApp -> RAN)	90.17	85.82	152.12	163.68
8. Decode & handle control	0.29	0.24	0.95	10.93
Total round-trip	173.11	134.66	252.68	274.21

Benchmarked on ubuntu-latest, Release build, ZMQ + IPC, ASN.1 APER.

[github-actions]

🔄 E2E dApp Integration Results (commit a4c1818)

posix/ipc

• dApp exit: 0
• Indications received: 7

posix/tcp

• dApp exit: 0
• Indications received: 7

zmq/ipc

• dApp exit: 0
• Indications received: 7

zmq/tcp

• dApp exit: 0
• Indications received: 7

example_simple_agent + example_simple_dapp on ubuntu-latest, Release build

[github-actions]

🔀 E2E Topologies — multi-dApp / multi-RAN (commit a4c1818)

zmq/ipc

• ✅ 1 RAN - 1 dApp: indications=5
  • dapp peer=t11 ran=ran-solo sub=1 indications=5 seq=[0..4] dropped=0 (0%) age_ms(avg=0 max=0 @seq=0) hist[<=1:5 2-5:0 6-10:0 >10:0]
• ✅ 1 RAN - 2 dApps: dApp#1 ind=5 sub=1, dApp#2 ind=6 sub=2, RAN saw 2 dApps
  • dapp1 peer=t12 ran=ran-shared sub=1 indications=5 seq=[0..4] dropped=0 (0%) age_ms(avg=0 max=0 @seq=0) hist[<=1:5 2-5:0 6-10:0 >10:0]
  • dapp2 peer=t12 ran=ran-shared sub=2 indications=6 seq=[0..5] dropped=0 (0%) age_ms(avg=0 max=0 @seq=0) hist[<=1:6 2-5:0 6-10:0 >10:0]
• ✅ 2 RANs - 1 dApp: from ran-a ind=5, from ran-b ind=5
  • dapp peer=t2a ran=ran-a sub=1 indications=5 seq=[0..4] dropped=0 (0%) age_ms(avg=0 max=0 @seq=0) hist[<=1:5 2-5:0 6-10:0 >10:0]
  • dapp peer=t2b ran=ran-b sub=1 indications=5 seq=[0..4] dropped=0 (0%) age_ms(avg=0 max=0 @seq=0) hist[<=1:5 2-5:0 6-10:0 >10:0]

zmq/tcp

• ✅ 1 RAN - 1 dApp: indications=5
  • dapp peer=default ran=ran-solo sub=1 indications=5 seq=[0..4] dropped=0 (0%) age_ms(avg=0 max=0 @seq=0) hist[<=1:5 2-5:0 6-10:0 >10:0]
• ✅ 1 RAN - 2 dApps: dApp#1 ind=5 sub=1, dApp#2 ind=6 sub=2, RAN saw 2 dApps
  • dapp1 peer=default ran=ran-shared sub=1 indications=5 seq=[0..4] dropped=0 (0%) age_ms(avg=0 max=0 @seq=0) hist[<=1:5 2-5:0 6-10:0 >10:0]
  • dapp2 peer=default ran=ran-shared sub=2 indications=6 seq=[0..5] dropped=0 (0%) age_ms(avg=0 max=0 @seq=0) hist[<=1:6 2-5:0 6-10:0 >10:0]
• ✅ 2 RANs - 1 dApp: from ran-a ind=5, from ran-b ind=5
  • dapp peer=default ran=ran-a sub=1 indications=5 seq=[0..4] dropped=0 (0%) age_ms(avg=0 max=0 @seq=0) hist[<=1:5 2-5:0 6-10:0 >10:0]
  • dapp peer=off100 ran=ran-b sub=1 indications=5 seq=[0..4] dropped=0 (0%) age_ms(avg=0 max=0 @seq=0) hist[<=1:5 2-5:0 6-10:0 >10:0]

example_simple_agent + example_simple_dapp on ubuntu-latest, Release. Indication age is report-only.

[Thecave3]

Closing as superseded by latrec (#59), landed via #55.

The [LAT] log markers here are a strict subset of the 18 stages latrec
already ships (now 23, after this PR): every stage this PR adds is one
latrec_tstamp() call — one clock_gettime(CLOCK_MONOTONIC) and four
stores — versus a formatted logger line, which perturbs the sub-millisecond
path it measures by orders of magnitude more. anchor_ns is 0 at every call
site here, so there's no per-message key to correlate on beyond positional
line pairing, and this PR has no tests or reader. Nothing here needs to carry
forward.

Thanks for the exploration — the boundary choices (send/receive/dispatch)
were a useful reference point while designing latrec's own stage catalog.