release: adopt pi 0.84.4 + pi-atelier v0.10.0, and fix the doc claim the pi bump invalidates

pi 0.84.3 -> 0.84.4 (no Breaking Changes / Removed heading in that section,
grepped). Adopted for three fixes that land on machinery this fleet runs:
#6879 (large tool results crossing the auto-compaction threshold were sent to
the provider before compacting), #8345 (a resumed session corrupted its next
appended entry when the JSONL lacked a trailing newline -- that file is the
memory feeder's input; measured 49/49 clean here beforehand), and #8537
(triggerTurn:false messages sent mid-run were inserted between a tool call and
its result). The mempalace mailbox is outside #8537's precondition: it delivers
at agent_settled with deliverAs:"steer" and no triggerTurn, and 0.84.4 leaves
the documented steer semantics unchanged.

pi-atelier v0.8.2 -> v0.10.0: two minor releases, both UI-only, no BREAKING
notice. v0.9.0 raises its minimum pi to 0.84.0 and, unlike the
0.7.1-under-pi-0.84 startup-hang precedent, encodes it in peerDependencies
(>=0.84.0). Satisfied by PI_VERSION=0.84.4. Both executable floors compare with
sort -V, so 0.10.0 >= 0.7.1 evaluates correctly.

docs/observational-memory.md: pi's own compaction.md gained one paragraph in
0.84.4 -- autoCompact is now also checked mid-run, after a tool batch's results
are appended. Our text said compaction is checked only when pi goes idle and so
"never interrupts a turn"; that was only ever true of the OM trigger. The
section now states both entry points into session_before_compact and the
diagram carries the second edge (mermaid checker re-run: 6 blocks, 44 labels,
0 soft-wrapped, no cut glyphs at 1280px and 800px).

README: the version-pin table had been wrong since v1.8.6 -- 93f986e moved
ARG PI_VERSION to 0.84.3 and MEMPALACE_VERSION to 3.8.0 and neither table row,
so it advertised pi 0.84.2 / mempalace 3.7.1. Corrected, plus the
--expected-version example that would now fail against a 0.84.4 image.

CHANGELOG: Unreleased retitled v1.8.12 (2026-08-31) with the audits above and a
dependency-audit table -- every other component measured SAME (skillset
snapshot --check OK at a12fe5e, 0 commits since baked).

README.md

@@ -1093,7 +1093,7 @@ persisted volumes survived, and pi runtime wiring is intact:
 ```bash
 ./scripts/recreate-sanity-check.sh                              # auto-detects variant
 ./scripts/recreate-sanity-check.sh --expected-image-version 1.8.9  # assert the pi-devbox release tag
-./scripts/recreate-sanity-check.sh --expected-version 0.84.3        # assert the pi coding agent version
+./scripts/recreate-sanity-check.sh --expected-version 0.84.4        # assert the pi coding agent version
 ```
 
 Those are **two different versions**, and the flags are not interchangeable:
@@ -1132,9 +1132,9 @@ resolved to `latest` at build time:
 
 | Component | Pin | Where |
 |---|---|---|
-| pi | `0.84.2` | `ARG PI_VERSION` — `Dockerfile.variant` |
-| pi-atelier | `v0.8.2` | `ARG PI_ATELIER_REF` — `Dockerfile.variant` |
-| mempalace | `3.7.1` | `ARG MEMPALACE_VERSION` — `Dockerfile.base` |
+| pi | `0.84.4` | `ARG PI_VERSION` — `Dockerfile.variant` |
+| pi-atelier | `v0.10.0` | `ARG PI_ATELIER_REF` — `Dockerfile.variant` |
+| mempalace | `3.8.0` | `ARG MEMPALACE_VERSION` — `Dockerfile.base` |
 
 The objective is **not** to freeze versions. Bumping is routine — usually one
 line plus a changelog note. The objective is that adopting a new upstream