The scenario's success criterion existed only as a comment: count
"Parent switched" in n04's log, expect at most 5. Nothing read it, and
the scenario declared no assertions at all, so its exit code could only
report that the mesh came up and nothing crashed.
Add a max_parent_switches assertion and wire that criterion to it.
The assertion takes an optional node scope, which is the part that
matters. The existing sibling counts mesh-wide, and a criterion written
about one node's log is a different quantity from the sum over every
node: across archived runs of this scenario n04 is 1 or 2 while the
mesh-wide total ranges 3 to 6. Asserting the sum against a per-node
threshold would check something other than what was specified, and at
this threshold would also have failed several runs that were fine.
Counting nothing must not read as stability. A node id absent from the
topology fails explicitly rather than matching zero log lines and
sailing under the ceiling, and a scenario that declares a parent-switch
assertion while setting a log level that suppresses the events it counts
is rejected at load rather than passing vacuously after a full run. The
parse rejects a mistyped key, a missing, negative, boolean or
non-integer ceiling, and a node written empty or as a non-string -- that
last one because YAML renders a bare `node:` as null, which would
silently revert to the mesh-wide count.
The scenario comment now records what the threshold is worth against
the 11 completed archived runs rather than a single sample: 5 is well
above anything observed, the daemon's own parent hold-down caps
switches near 6 per run, and nearly every switch lands during initial
tree formation before any mutation fires. So this catches only
near-pathological reparenting. Tightening to 3 would make it a real
detector, but that changes the stated criterion rather than fixing it,
so it is left as a decision.
Verified against a live run: the assertion evaluates n04 at 2 against
mesh-wide 4 and passes, and with the ceiling temporarily set to 0 the
scenario exits 3, the assertion-failure code, which it previously could
not reach.
Cost-based parent selection:
- Replace depth-only parent selection with effective_depth = depth + link_cost
- link_cost computed from locally measured MMP metrics: etx * (1.0 + srtt_ms / 100.0)
- Prevents bottleneck subtrees in heterogeneous networks where a LoRa link
at depth 1 would otherwise always beat fiber at depth 2
- Configurable hysteresis (default 0.2) prevents marginal parent switches
- Configurable hold-down timer (default 30s) suppresses re-evaluation
after parent switch
- Mandatory switches (parent lost, root change) bypass both safeguards
- Link costs passed as HashMap parameter to keep TreeState pure
Periodic re-evaluation:
- evaluate_parent() was only called on TreeAnnounce receipt or parent loss;
after tree stabilization, link degradation went undetected
- Added timer-based re-evaluation (reeval_interval_secs, default 60s) that
calls evaluate_parent() from the tick handler with current MMP link costs
- Respects existing hold-down and hysteresis safeguards
- Short-circuits when disabled or <2 peers
Design documentation:
- Update 7 design docs to reflect cost-based parent selection
- Replace depth-only algorithm descriptions with effective_depth model
- Replace rejected cumulative path cost spec with local-only design rationale
- Rewrite Example 2 (heterogeneous links) for local-only cost model
- Update config docs: parent_switch_threshold replaced by parent_hysteresis,
hold_down_secs, reeval_interval_secs
Chaos simulation enhancements:
- fips_overrides with deep merge for per-scenario FIPS config customization
- Explicit topology algorithm for deterministic test graphs
- Control socket querying via fipsctl for tree/MMP snapshot collection
- Edge existence validation in netem manager
- Per-link netem policy overrides
- 9 new chaos scenarios covering cost avoidance, depth-vs-cost tradeoffs,
stability, mixed topologies, periodic re-evaluation, and bottleneck parent
12 new unit tests, 667 total passing, clippy clean.
Johnathan Corgan