feat(trace-topology): Rust trace-fixture generator (netns + TSN, v0.11.0)

[avrabe]

Summary

v0.11.0 PR 1. A Rust binary — gen-fixtures, in the spar-trace-topology crate — that produces the four runtime artefacts the reconciliation engine will test against, from a synthetic 3-node TSN topology (grandmaster / switch / endpoint) built in Linux network namespaces.

Why Rust, not a shell script

The maintainer's standing preference — and it earns its keep here:

• Typed config; Result error propagation with context on every fallible step.
• NetnsGuard RAII — Drop runs ip netns del, so a panic or ?-propagated error still tears the topology down. A shell trap silently no-ops on a crash and leaves stale /run/netns handles for the next run to collide with.
• The two transform steps are pure, unit-tested functions.

What it generates

Fixture	Source
capture.pcapng	tcpdump on the GM veth
lldp.json	lldpd -H 0 + lldpctl -f json
qcc-yang.json	tc taprio/cbs → tc -j qdisc show → transformed to the QccYangSwitchConfigSource shape
gptp.json	ptp4l + pmc → transformed to the GptpJsonPtpTimeSource shape

Two gotchas baked in from smithy's live testing: veths are created multi-queue (numtxqueues/numrxqueues 4) because sch_taprio rejects single-queue devices; taprio runs in software mode (flags 0x0) — no TSN NIC.

gPTP timestamp_ns is replaced by a deterministic synthetic counter (fixed epoch + step) so fixture diffs aren't noisy; sync_error_ns (abs master offset) is kept as observed. Qci stream-filters have no Linux kernel equivalent — synthesised from a static config, documented as such in the code.

Scope

Tool only. The 9 transformer unit tests run on any host (no netns dependency) and every generated JSON round-trips through the ingest.rs parsers. The CI harness that runs the netns-touching path is deliberately a follow-up: per the smithy QEMU enablement it'll be a KVM guest, not the netns runner — building that workflow now would be rework.

Test plan

• cargo build -p spar-trace-topology --bins clean
• cargo test -p spar-trace-topology — 34 tests pass (9 new transformer tests)
• cargo clippy -p spar-trace-topology --all-targets -- -D warnings clean
• cargo fmt --check clean
• rivet validate PASS
• CI green

Co-Authored-By: Claude Opus 4.7 noreply@anthropic.com

[github-actions]

Rivet verification gate

✅ 20/20 passed

	count
Passed	20
Failed	0
Skipped (no steps)	0

Filter: (and (= type "feature") (or (has-tag "v093") (has-tag "v0100")))

Failed artifacts

(none)

_{Updated automatically by tools/post_verification_comment.py. Source of truth: artifacts/verification.yaml.}

[codecov]

Codecov Report

❌ Patch coverage is 35.95166% with 424 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/spar-trace-topology/src/bin/gen-fixtures.rs	0.00%	271 Missing ⚠️
crates/spar-trace-topology/src/fixtures/netns.rs	0.00%	97 Missing ⚠️
crates/spar-trace-topology/src/fixtures/mod.rs	0.00%	34 Missing ⚠️
...ates/spar-trace-topology/src/fixtures/transform.rs	91.53%	22 Missing ⚠️

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