changelog: task tool + fork-gate (pi-extensions 25c1265), and the mine deadline that never reached the transport (mempalace-toolkit 817b3a8)

Both land in the image through floating refs (PI_EXTENSIONS_REF=main,
MEMPALACE_TOOLKIT_REF=main), so neither shows up as a diff in this repo — the
changelog is the only place a reader of a pi-devbox tag learns that the
container's delegation and feed behaviour changed. Recorded under Unreleased
with the measurements: 5/5 real fork briefs redirected, live pi -p proof for
gate and tool, 2-of-6 → 6-of-6 on the toolkit's new timeout test.

Dockerfile.base: the "Stall protection" comment listed MEMPALACE_MCP_TIMEOUT_MS
as THE tool-call deadline; it now says the feed's mine carries its own.
Comment-only, but Dockerfile.base is hashed into base_tag; the rebuild was
already forced by 50153e6 (rootfs/ skill floor).

Dockerfile.base

@@ -452,7 +452,10 @@ RUN ARCH=$(case "${TARGETARCH}" in amd64) echo "x86_64" ;; arm64) echo "aarch64"
 # uninterruptibly. A stall-kill is no longer a permanent latch either: the
 # next tool call respawns the server with capped exponential backoff (the
 # budget resets on any successful response). Tunables:
-# MEMPALACE_MCP_TIMEOUT_MS (default 60000), MEMPALACE_MCP_INIT_TIMEOUT_MS
+# MEMPALACE_MCP_TIMEOUT_MS (default 60000; the feed's `mempalace_mine` carries
+# its own longer MEMPALACE_FEED_MINE_TIMEOUT_MS, default 300000, since toolkit
+# 817b3a8 — before that the 60 s deadline cut every honest mine off),
+# MEMPALACE_MCP_INIT_TIMEOUT_MS
 # (default 300000 — generous so a genuine first cold-open isn't killed),
 # MEMPALACE_MCP_MAX_RESPAWNS (default 2; 0 disables self-heal),
 # MEMPALACE_MCP_RESPAWN_BACKOFF_MS (default 1000); timeouts of 0 disable.