Draft the Phase 8 processing design

Starts from the distribution channel and the safety invariant it
protects, and derives the language from them, rather than designing a
rule language and asking later how to ship it.

Four decisions proposed. A rule is a matcher plus ordered typed actions,
with no expressions and nothing resembling eval -- less expressive than
Cribl on purpose, and the only shape that can be pushed to ten thousand
hosts and audited by reading it. Total evaluation is the primary safety
guarantee, with apply-then-verify as a backstop. One spec with two
implementations means a language-neutral conformance suite is the
specification and should be built first, not last. Distribution reuses
DesiredOverride, following extra_file_paths as the precedent for a
repeated field.

It also corrects something #21 got wrong. That change said a fatal rule
would strand an agent the way a corrupted ingest endpoint does. Reading
apply_override's actual semantics, overrides live only in the running
process's memory and are never written to disk, so a restarted agent
boots clean and re-syncs -- a fatal rule set crash-loops rather than
strands, and the agent keeps checking in, so it stays correctable. That
is a much better failure mode, and it was acquired by accident: the
"don't persist" choice was made to avoid filesystem writes on read-only
images, not for safety. This design promotes it to a constraint, since
persisting overrides later would silently convert every crash-loop into
a strand. positioning.md is corrected to match rather than left
disagreeing.

Five open questions are left open rather than answered to look decisive,
the sharpest being that there is no staged rollout today: an edit
reaches every matching agent at once, which for executable rules is the
difference between breaking one host and breaking all of them.

The v1 acceptance test is real data, not a fixture: two processes on the
maintainer's own workstation account for 308 of 325 journal entries in
five minutes, and a suppress rule should remove about 60% of that host's
volume.

Signed-off-by: John Coffey <[email protected]>

docs/status.md

@@ -20,7 +20,7 @@ verification procedure and its results.
 | 5 | Frontend redesign and design system | Shipped |
 | 6 | License compliance audit and remediation | Shipped |
 | 7 | AI-assisted query authoring | Shipped |
-| 8 | Processing: rule DSL, agent-side and ingest-side, and its distribution | Planned |
+| 8 | Processing: rule DSL, agent-side and ingest-side, and its distribution | Planned, [design drafted](phase-8-processing-design.md) |
 | 9 | Routing: multiple destinations and delivery guarantees | Planned |
 | 10 | Archive and replay, tiering, automatic TTL | Planned |
 | — | Fleet: central agent configuration | Mostly shipped, see below |