diff --git a/context/test-evidence/tooling.md b/context/test-evidence/tooling.md
index 34319d67..c7c92df3 100644
--- a/context/test-evidence/tooling.md
+++ b/context/test-evidence/tooling.md
@@ -1731,3 +1731,44 @@ already requires the dev shell for `tpl`, and the dev shell's `stat` is GNU.
 From `ci.yml`, the toolchain version probes ("the dev shell supplies the pinned
 web toolchain", "Playwright matches the dev shell's browsers") and every
 `shell: bash` override, so every step runs in `nix develop .#ci`.
+
+### A thread past ARG_MAX is read from stdin — `scripts/pr-reviews-test.sh` (improvise-5jxt)
+
+**What broke.** `fetch` handed the review, inline-comment and issue-comment
+JSON to one `jq -n --argjson …` call as arguments. Once #210's comments
+outgrew the kernel's argument limit, `execve` refused to start jq:
+`jq: Argument list too long`, exit 126, with nothing printed. That happened
+with or without `--wait`. The script is how agents read reviews, so an ADR
+steward was blocked on it.
+
+**Fix.** A `combine` helper sends the three documents to `jq -s` on stdin
+through `printf`. `printf` is a bash builtin, so no `execve` sees the data.
+Both paths use `combine`: the fixture path and the live `gh` path. The other
+jq calls in `pr-reviews` already read `$json` from a pipe. `--arg head` carries
+only a 40-character SHA.
+
+**The fixture.** Each of the three surfaces carries about 2 MB: a review body,
+an inline comment followed by a small one after it, and an issue comment. 2 MB
+exceeds both macOS's total `ARG_MAX` (1 MB) and Linux's per-argument
+`MAX_ARG_STRLEN` (128 KB). Every surface is large, so a fix that moves only one
+document off argv still fails. The file is built with `head -c`, `tr` and
+`printf`, so it depends on no tool version and no path.
+
+**Red first.** Before the fix, "a thread larger than ARG_MAX is still read" and
+"… still satisfies --wait" exited 126, as #210 did live.
+
+**Rivals** (each 25 passed, 5 failed; the five are the new cases):
+- **The pre-fix script**, restored from `gh/main`: exit 126 on both run cases,
+  and all three print assertions miss.
+- **A partial fix** that pipes the review and inline documents but still
+  passes the issue comments with `--argjson issue "$3"`: also exit 126. So the
+  large issue fixture is load-bearing, not decoration.
+
+**Live.** `./scripts/pr-reviews 210` exits 0 with its output sent to a file.
+The output includes the user's inline answers on
+`context/adr/007-stable-identities.md` from 2026-09-24T19:50:22Z onward
+("full unicode", "Just a plane number.", …).
+
+**Scope sweep.** `scripts/pr-watch` passes its JSON through `printf '%s' | jq`,
+never as an argument. `grep -rn 'argjson\|--arg '` over `scripts/`,
+`.agents/` and `.claude/skills/` finds no other data argument.
diff --git a/scripts/pr-reviews b/scripts/pr-reviews
index 55de7185..298a7687 100755
--- a/scripts/pr-reviews
+++ b/scripts/pr-reviews
@@ -87,28 +87,32 @@ fixture_file() {
 }
 
 # `gh api --paginate` emits one JSON array PER PAGE, so a comment thread past
-# the page size arrives as several concatenated documents that --argjson
-# rejects. Both paths flatten through here, so a fixture can carry two pages.
+# the page size arrives as several concatenated documents that combine
+# would misnumber. Both paths flatten through here, so a fixture can carry two pages.
 pages_to_array() { jq -s 'add // []'; }
 
+# The three documents reach jq on STDIN, never as --argjson: a thread past
+# ARG_MAX is exit 126 before jq runs (improvise-5jxt). printf is a builtin.
+combine() {
+  printf '%s\n%s\n%s\n' "$1" "$2" "$3" | jq -s \
+    '{head: (.[0].headRefOid // ""), reviews: (.[0].reviews // []),
+      inline: .[1], issue: .[2]}'
+}
+
 fetch() {
   if [ -n "${PR_REVIEWS_FIXTURE_DIR:-}" ]; then
     local n; n=$(fixture_poll)
     local pr; pr=$(fixture_file "$n" pr)
     local inline; inline=$(fixture_file "$n" inline | pages_to_array)
     local issue; issue=$(fixture_file "$n" issue | pages_to_array)
-    jq -n --argjson pr "$pr" --argjson inline "$inline" --argjson issue "$issue" \
-      '{head: ($pr.headRefOid // ""), reviews: ($pr.reviews // []),
-        inline: $inline, issue: $issue}'
+    combine "$pr" "$inline" "$issue"
     return
   fi
   local repo; repo=$(gh_ repo view --json nameWithOwner -q .nameWithOwner)
   local pr; pr=$(gh_ pr view "$PR" --json headRefOid,reviews)
   local inline; inline=$(gh_ api "repos/$repo/pulls/$PR/comments" --paginate | pages_to_array)
   local issue; issue=$(gh_ api "repos/$repo/issues/$PR/comments" --paginate | pages_to_array)
-  jq -n --argjson pr "$pr" --argjson inline "$inline" --argjson issue "$issue" \
-    '{head: ($pr.headRefOid // ""), reviews: ($pr.reviews // []),
-      inline: $inline, issue: $issue}'
+  combine "$pr" "$inline" "$issue"
 }
 
 # `line` is null once the line has moved under the comment; `original_line` is
diff --git a/scripts/pr-reviews-test.sh b/scripts/pr-reviews-test.sh
index 5050958d..a5294069 100755
--- a/scripts/pr-reviews-test.sh
+++ b/scripts/pr-reviews-test.sh
@@ -291,6 +291,32 @@ prints "a comment on the first page survives pagination" "$d" 'page1\.rs:1'
 prints "a comment on the second page survives pagination" "$d" 'page2\.rs:2'
 run_case "a paginated thread still satisfies --wait" 0 "$d" --wait 1 --interval 1
 
+# ---------------------------------------------------------------------------
+# A thread past ARG_MAX (improvise-5jxt). PR #210's comments outgrew the argv
+# limit, and a fetch that hands the JSON to jq as an argument dies with exit
+# 126 before printing anything. 2MB per surface clears every platform's limit,
+# and EACH surface is large, so a fix that moves only one of them off argv fails.
+d="$work/huge"
+mkdir -p "$d"
+big=$(head -c 2000000 /dev/zero | tr '\0' x)
+{ printf '{"headRefOid":"%s","reviews":[{"state":"COMMENTED",' "$HEAD"
+  printf '"submittedAt":"2026-09-22T09:00:00Z","author":{"login":"owner"},'
+  printf '"commit":{"oid":"%s"},"body":"BIGREVIEW %s"}]}\n' "$OLD" "$big"
+} > "$d/last.pr.json"
+{ printf '[{"created_at":"2026-09-22T10:00:00Z","user":{"login":"owner"},"commit_id":"%s",' "$HEAD"
+  printf '"path":"big.rs","line":1,"body":"%s"},\n' "$big"
+  printf '{"created_at":"2026-09-22T10:00:01Z","user":{"login":"owner"},"commit_id":"%s",' "$HEAD"
+  printf '"path":"after.rs","line":9,"body":"AFTERTHEBIGONE"}]\n'
+} > "$d/last.inline.json"
+printf '[{"created_at":"2026-09-22T11:00:00Z","user":{"login":"owner"},"body":"BIGISSUE %s"}]\n' \
+  "$big" > "$d/last.issue.json"
+unset big
+run_case "a thread larger than ARG_MAX is still read" 0 "$d"
+prints "a comment after a multi-MB one is printed" "$d" 'after\.rs:9 commit=aaaaaaaa <- CURRENT HEAD'
+prints "a multi-MB review body is printed" "$d" 'BIGREVIEW x'
+prints "a multi-MB issue comment is printed" "$d" 'BIGISSUE x'
+run_case "a thread larger than ARG_MAX still satisfies --wait" 0 "$d" --wait 1 --interval 1
+
 # ---------------------------------------------------------------------------
 # Usage is exit 4 and must stay there: briefs distinguish it from 1.
 rm -f "$work/empty/.poll"