briefings: mod-loop — cut/backtracking allowance + sx_write_file-first + loaded-env/not(Goal) gotchas

Make explicit that the loop may lean on Prolog backtracking (pl-query-all) and cut,
preferring clause-order precedence via pl-query-one. Default to sx_write_file over
path/pattern edits; flag that sx_insert_near drops all but the first form. Document
the loaded-env primitive restriction (includes?/chars/etc. undefined after prolog
preloads; use the tokenizer's surviving set) and that negation is the not(Goal)
functor, not the prefix \+ operator.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plans/agent-briefings/mod-loop.md

@@ -66,7 +66,12 @@ Every iteration: implement → test → commit → tick `[ ]` → Progress log
   like a broken binary but is just a param mismatch. `sx_validate` after edits.
   Path-based edits (`sx_replace_node`) count comment headers in their indices and
   can clobber the wrong node — re-read after, or prefer `sx_write_file` for small
-  files.
+  files. **Default to `sx_write_file` (rewrite the whole file) over path/pattern
+  edits** — these are small files and the rewrite always parses-before-writing.
+  `sx_insert_near` inserts only the FIRST top-level form of a multi-form source
+  (it silently drops the rest; byte count barely moves) — never use it to add a
+  block of forms; rewrite the file instead. `sx_replace_by_pattern` is fiddly to
+  match — don't fight it, just rewrite.
 - **Unicode in `.sx`:** raw UTF-8 only, never `\uXXXX` escapes.
 - **Commit granularity:** one feature per commit. Short factual messages
   (`mod: spam-keyword policy rule → :hide + 6 tests`). Push to `origin/loops/mod`.
@@ -82,8 +87,30 @@ Every iteration: implement → test → commit → tick `[ ]` → Progress log
   precedence explicit and deterministic (tests will depend on it). A "no rule
   matched" outcome must be a real, testable result (`:keep`), not a query failure
   you forget to handle.
+- **You may lean on backtracking and cut.** The substrate is full Prolog —
+  `pl-query-all` gives every proven clause (use it for "strictest-wins" or
+  multi-match analysis), `pl-query-one` gives the first (clause order = precedence).
+  Cut (`!`) and the other control constructs are available if you need to prune
+  alternatives inside a body, but for rule precedence prefer plain clause ordering
+  resolved by `pl-query-one` — it's the clean, testable default. Don't hand-roll
+  precedence in SX when the engine's backtracking already gives it to you.
 - **Negative decisions need closed-world care.** "No evidence of violation" vs
   "evidence absent" differ. Be explicit about negation-as-failure where you use it.
+  In this substrate, negation is the **functor** `not(Goal)` / `\+(Goal)` — the
+  prefix `\+ Goal` operator does **not** parse. Unknown predicates *fail* (no
+  existence error), so a report lacking some fact safely falls through a rule that
+  references it. Quote user-data atoms (`'foo-bar'`) — a bare hyphen is the minus
+  operator and will misparse.
+- **Loaded-env strips the high-level string prims.** After the prolog preloads are
+  loaded, the eval env loses `includes?`, `chars`, `str-join`, `keyword` and
+  friends — they are **undefined** (a function calling one fails only when called,
+  often mid-test-load, looking like a mystery crash). Only the set the Prolog
+  tokenizer itself uses survives: `slice`, `len`, `nth`, `=`, `join` (sep first:
+  `(join sep list)`), `downcase`, `map`, `reduce`, `append`/`append!`, `when`,
+  `cond`, `if`, `let`, `begin`, `get`, `dict-get`, `keys`, `empty?`, `first`,
+  `reverse`, `+`, `-`, `<`, `<=`. Build substring search yourself over `slice`/
+  `len` (see `mod/str-contains?`). Treat `not`, `and`, `or`, `>` as suspect in
+  guest code unless you've confirmed them — nest `if`/`when` and use `(< a b)`.
 - **Lifecycle state is separate from policy.** Keep the state machine (Phase 3) as
   an SX module over the engine, not tangled into Prolog rules.
 - **Federation trust is advisory by default.** A peer's decision only binds locally