fix: missing sawMessage init in accumulator literal; add pre-commit port typecheck hook

The CI port job's tsc --noEmit caught SessionEventAccumulator literals not
initializing the new sawMessage field (tests don't typecheck, so bun test
was green). Add a committed .githooks/pre-commit that mirrors the CI port
job — regenerate the port into a temp dir and tsc --noEmit it — so this
class of error fails at commit time, not in CI.

.githooks/pre-commit

@@ -0,0 +1,37 @@
+#!/bin/sh
+# pre-commit — typecheck the generated omp port before committing.
+#
+# Mirrors the CI port job (.gitea/workflows/port-to-omp.yml). The source
+# repo's own tsconfig extends the host harness tsconfig and is not
+# self-contained, so the reliable typecheck target is the regenerated port:
+# it ships a self-contained tsconfig and the pinned @oh-my-pi SDK as a real
+# devDependency. Regenerating into a temp dir and running `tsc --noEmit`
+# there catches exactly what CI will fail on (e.g. an interface field added
+# without updating its object literals).
+#
+# Enable (per clone):  git config core.hooksPath .githooks
+set -euo pipefail
+
+ROOT="$(git rev-parse --show-toplevel)"
+cd "$ROOT"
+
+# Fast path: no TypeScript-adjacent change staged -> nothing to typecheck.
+if git diff --cached --quiet -- src/ agents/ package.json tsconfig.json port-to-omp.mjs; then
+  exit 0
+fi
+
+TMP="$(mktemp -d)"
+LOG="$(mktemp)"
+trap 'rm -rf "$TMP" "$LOG"' EXIT
+
+if ! bun port-to-omp.mjs --out "$TMP" >"$LOG" 2>&1; then
+  echo "pre-commit: port regeneration failed (CI would fail too) — output:" >&2
+  tail -20 "$LOG" >&2
+  exit 1
+fi
+
+if ! (cd "$TMP" && bun run typecheck) >"$LOG" 2>&1; then
+  echo "pre-commit: port typecheck failed (this is what CI runs) — output:" >&2
+  tail -30 "$LOG" >&2
+  exit 1
+fi