diff --git a/.github/workflows/cross-repo-issue-closer.yml b/.github/workflows/cross-repo-issue-closer.yml
index b82103bcb04..d6a4c4a5137 100644
--- a/.github/workflows/cross-repo-issue-closer.yml
+++ b/.github/workflows/cross-repo-issue-closer.yml
@@ -162,10 +162,21 @@ jobs:
           # to fail instead of one. It still fails, and the loop still names the
           # target it failed on.
           #
-          # 400/401/404/422 stay exempt: a malformed request, a wrong target, or a
-          # body past GitHub's 65536-character comment limit is this repo's own
-          # bug. It is answered correctly on the first try and asking again only
-          # spends runner minutes.
+          # 400/401/404/422 stay exempt: a malformed request, a wrong target, or
+          # an oversized body is this repo's own bug. It is answered correctly on
+          # the first try and asking again only spends runner minutes.
+          #
+          # Both caps this step can hit are MEASURED, in UTF-8 BYTES, and they are
+          # the same number — ⛔ neither is the 65,536 characters this comment used
+          # to name. A COMMENT (`issues.createComment` below) stores 262,144 bytes
+          # and refuses 262,145 with a real 422: objectstack#18826, bisected to one
+          # byte. An ISSUE BODY (`issues.update` below) stores 262,144 and refuses
+          # 262,145 SILENTLY — 200, old body kept, nothing reported:
+          # objectstack#18793, bisected to one byte, restated as
+          # `ISSUE_BODY_LIMIT` in scripts/pm/check-half-states.mjs. ⛔ Do not
+          # re-derive 65,536 from a refusal message: GitHub's own 422 text still
+          # says "maximum is 65536 characters" and #18826 falsified it in both unit
+          # and value by storing a 262,144-character comment.
           retries: 3
           retry-exempt-status-codes: 400,401,404,422
           script: |
diff --git a/.github/workflows/docs-drift-check.yml b/.github/workflows/docs-drift-check.yml
index 87f929eec9c..47175bbc9d3 100644
--- a/.github/workflows/docs-drift-check.yml
+++ b/.github/workflows/docs-drift-check.yml
@@ -554,9 +554,17 @@ jobs:
             //        separates it from a genuine permission denial.
             // Everything else stays fatal on purpose: 401 / plain 403 (the `permissions:`
             // block above is wrong), 404 (wrong target), 422 (the body this workflow built
-            // is not postable — e.g. past GitHub's 65536-character comment limit), and any
-            // non-HTTP error such as a TypeError in the code above. Those are this repo's
-            // own bugs and must keep failing the job.
+            // is not postable — e.g. past the COMMENT cap), and any non-HTTP error such as
+            // a TypeError in the code above. Those are this repo's own bugs and must keep
+            // failing the job.
+            //
+            // That cap is MEASURED, in UTF-8 BYTES, ⛔ not the 65,536 characters this
+            // comment used to name: a comment stores 262,144 bytes and refuses 262,145
+            // with a real 422, on BOTH `issues.createComment` and `issues.updateComment`
+            // below — objectstack#18826, bisected to one byte on each endpoint. ⛔ Do not
+            // re-derive 65,536 from the refusal itself: GitHub's own 422 text still reads
+            // "maximum is 65536 characters" and #18826 falsified it in both unit and
+            // value, storing a 262,144-CHARACTER comment.
             const TRANSIENT_NETWORK_CODES = new Set([
               'ECONNRESET', 'ECONNREFUSED', 'ETIMEDOUT', 'EAI_AGAIN', 'ENOTFOUND', 'EPIPE',
               'EHOSTUNREACH', 'ENETUNREACH', 'UND_ERR_SOCKET', 'UND_ERR_CONNECT_TIMEOUT',
diff --git a/.github/workflows/merge-queue-triage.yml b/.github/workflows/merge-queue-triage.yml
index d649bb99613..60d87161a49 100644
--- a/.github/workflows/merge-queue-triage.yml
+++ b/.github/workflows/merge-queue-triage.yml
@@ -174,9 +174,22 @@ jobs:
           # wrong `permissions:` block) now takes four attempts to fail instead of
           # one. It still fails.
           #
-          # 400/401/404/422 stay exempt: a malformed request, a wrong target, or a
-          # body past GitHub's 65536-character comment limit is this repo's own bug,
-          # answered on the first try and not improved by asking again.
+          # 400/401/404/422 stay exempt: a malformed request, a wrong target, or
+          # an oversized body is this repo's own bug, answered on the first try and
+          # not improved by asking again.
+          #
+          # Both caps this workflow can hit are MEASURED, in UTF-8 BYTES, and they
+          # are the same number — ⛔ neither is the 65,536 characters this comment
+          # used to name. A COMMENT (`issues.createComment` below) stores 262,144
+          # bytes and refuses 262,145 with a real 422: objectstack#18826, bisected
+          # to one byte. An ISSUE BODY (`issues.update` / `issues.create` below)
+          # stores 262,144 and refuses 262,145 — on `create` with a 422 (#18826),
+          # on `update` SILENTLY, 200 with the old body kept and nothing reported:
+          # objectstack#18793, bisected to one byte, restated as
+          # `ISSUE_BODY_LIMIT` in scripts/pm/check-half-states.mjs. ⛔ Do not
+          # re-derive 65,536 from a refusal message: GitHub's own 422 text still
+          # says "maximum is 65536 characters" and #18826 falsified it in both unit
+          # and value by storing a 262,144-character comment.
           retries: 3
           retry-exempt-status-codes: 400,401,404,422
           script: |
diff --git a/.github/workflows/scheduled-full-run-card.yml b/.github/workflows/scheduled-full-run-card.yml
index af34c81d8d2..1e3b9bfac60 100644
--- a/.github/workflows/scheduled-full-run-card.yml
+++ b/.github/workflows/scheduled-full-run-card.yml
@@ -121,9 +121,22 @@ jobs:
           # Same transient-retry posture as merge-queue-triage.yml, and for the
           # same reason: 403 is REMOVED from the exempt list because GitHub
           # answers a secondary rate limit with 403 as well as 429, and this job
-          # pages issues. 400/401/404/422 stay exempt — a malformed request or a
-          # body past the 65536-character limit is this repo's own bug and is
-          # not improved by asking again.
+          # pages issues. 400/401/404/422 stay exempt — a malformed request or
+          # an oversized body is this repo's own bug and is not improved by
+          # asking again. The size that makes a body oversized is MEASURED, in
+          # UTF-8 BYTES: this job writes an ISSUE BODY, which stores 262,144
+          # bytes and refuses 262,145 (objectstack#18793, bisected to one byte;
+          # restated as `ISSUE_BODY_LIMIT` in scripts/pm/check-half-states.mjs).
+          # ⛔ Not the 65,536 characters this comment used to name, and ⛔ not
+          # the number in GitHub's own refusal text either — that string still
+          # reads "maximum is 65536 characters" and objectstack#18826 falsified
+          # it in both unit and value by storing a 262,144-character comment.
+          # ⚠️ On `issues.update` an oversized body is not a 422 at all: the
+          # platform answers 200, keeps the OLD body and reports nothing
+          # (#18793). The 422 exemption stays right for the malformed request it
+          # also covers, and `issues.create` DOES answer 422 on an oversized
+          # body (#18826) — but ⛔ a refresh that outgrows the cap never reaches
+          # it.
           retries: 3
           retry-exempt-status-codes: 400,401,404,422
           script: |
diff --git a/.github/workflows/test-nightly-tiers.yml b/.github/workflows/test-nightly-tiers.yml
index 2eb37dc1b65..75a166b715f 100644
--- a/.github/workflows/test-nightly-tiers.yml
+++ b/.github/workflows/test-nightly-tiers.yml
@@ -433,8 +433,19 @@ jobs:
             const failing = read('failing-files.txt').split('\n').map((s) => s.trim()).filter(Boolean);
             const extractorExit = process.env.FAILING_FILES_EXIT;
 
-            // The log tails, bounded: a GitHub issue body caps at 65536 chars,
-            // and the run link carries the whole log anyway.
+            // The log tails, bounded. ⛔ The bound below is NOT the platform
+            // cap, and the platform cap is not 65,536 of anything. This step
+            // posts an ISSUE BODY, and that surface is MEASURED, in UTF-8
+            // BYTES: 262,144 bytes stored, 262,145 refused — bisected to one
+            // byte on objectstack#18793, and restated as `ISSUE_BODY_LIMIT` in
+            // scripts/pm/check-half-states.mjs. ⛔ Do not re-derive 65,536 from
+            // a refusal message: GitHub's own 422 text still says "maximum is
+            // 65536 characters" and is false in both unit and value —
+            // objectstack#18826 stored a 262,144-CHARACTER comment. ⚠️ And on
+            // this surface the refusal is not a 422 at all: an oversized issue
+            // body is answered 200 with the OLD body kept and nothing reported
+            // (#18793), so a body that outgrows the cap vanishes silently.
+            // The run link carries the whole log anyway.
             const tails = [];
             const reportsDir = path.join(process.env.RUNNER_TEMP, 'nightly-reports');
             const walk = (dir) => {
@@ -447,6 +458,16 @@ jobs:
               }
             };
             walk(reportsDir);
+            // BUDGET is a READING budget, ⛔ not a platform bound, and it is
+            // deliberately NOT re-sized now that the cap above is known to be
+            // four times what this file used to assert. 40,000 is about as much
+            // log tail as a person reads off a card before clicking through,
+            // and the run link carries every byte elided here — so this number
+            // is sized against the reader, and a correction to the cap moves a
+            // reading, never a licence to print more. It is counted in the unit
+            // the slice below uses (JS string length, i.e. UTF-16 code units),
+            // because nothing judges it against the byte cap: even as bytes of
+            // CJK prose it stays far under 262,144.
             const BUDGET = 40000;
             const perTail = Math.max(2000, Math.floor(BUDGET / Math.max(1, tails.length)));
             const tailBlocks = tails.sort((a, b) => a.shard.localeCompare(b.shard)).flatMap(({ shard, text }) => [