Volatile env/context text (git status, cwd, date) rode in req.system —
BEFORE the slab anchor in Anthropic's prefix order (tools → system →
messages) — so any git-state change cold-restarted the entire anchored
prefix. Telemetry attribution (events.jsonl 2026-06-26..07-02): 48.8%
of cold-create waste, ~2.6k tokens/session vs ~200 saved by imaging it.
Now appended as a trailing text block on the LAST user message — the
per-turn live tail that re-caches incrementally anyway — placed AFTER
history collapse (never baked into frozen chunks) and after tool_result
compression. Session-stable billingLine/sysRemainder stay in system;
fallback keeps env in system when no user message exists to carry it.
New telemetry field: envRelocatedChars.
Fix#1 (cross-session cache bust): strip the volatile "# Environment"
markdown section (working dir, git status, platform, model ID) out of
the system text BEFORE the static/dynamic split. It carries no XML
wrapper so splitStaticDynamic couldn't catch it, and its git-status
lines change across sessions - baking them into the slab PNG busted
the cross-session cache (system_sha8 717f1fce -> 5efaa4bb for a
one-file edit). Parallel to stripBillingLine: the section re-enters
the system tail as plain text.
Schema handling simplified, knob removed: the Anthropic text-reference
path now renders prose-only tool docs (schemas stay untouched in
tools[] - duplicating them in the reference was pure bloat), while the
GPT imaged path always carries the compact schema (there it IS the
compression). Deletes the {type:'object'} stub + SCHEMA_STRUCTURAL_KEYS
machinery, stripSchemaDescriptions import, and the COMPRESS_SCHEMAS env.
Tests: e2e regressions for anchor relocation onto byte-frozen carry-over
history images and first-collapse anchor staying on the slab; history
relocation fixture grown past the collapseChunk=50 snap (56 messages ->
cutoff 50, frozen windows 11/21/31/41, collapsedTurns 49 - the old
35-message fixture floored to one window and never froze a chunk).
tsc clean; 615/615 tests pass.
Intermittent prefix-cache busts on long sessions (#11): the single cache
breakpoint relocated onto the LAST history image — the still-growing chunk
whose bytes change every window advance — so the slab+history prefix
re-created at 1.25x instead of being read.
- relocateAnchorToHistoryImage pins collapseHistory's carry-over ordinal
(the last byte-stable chunk) instead of the last image.
- demoteProtectedHeadText keeps pxpipe's slab scaffolding (images +
fact-sheet + the [End of rendered context.] boundary) verbatim and only
quarantines the user's stale opening turn, so the relocator can still
find the slab anchor (#14 demotion had clobbered the boundary it keys on).
- cachePrefixDigest joins parts with \x00 so block-boundary differences
can't hash-collide into false prefix-stability.
520/520 green, tsc clean.
teamchong