ceremony/docs/RUNNER-PROBES.md

# Runner probes

**Not a drill.** A drill rehearses the release doors on a disposable repo and
ends. This is the opposite shape: one **standing** repo that exists so that
runner-only facts can be measured on demand, and it is **never archived**.

`heavy-duty/ceremony-runner-probe` — private, standing, reset between probes.
Ruled by the operator as option (A) of ceremony#202 (#5631).

## Why a standing repo, when drills are disposable

Some facts are only true inside Actions, under the token Actions injects, and
no local harness or PAT can reproduce them. The worked example is ceremony#192:

```
DELETE /issues/{n}/labels/{id}   ->  500   under ${{ github.token }} in a workflow
DELETE /issues/{n}/labels/{id}   ->  204   under a maintainer PAT, same call
```

A probe that runs anywhere else passes and proves nothing. Before this venue
existed the answer was "un-archive a drill repo", which was requested three
times in two days across two issues and never became anything — the three
drill repos (`ceremony-drill-0.4.1`, `-0.4.1-final`, `-191`) are all archived,
and each was minted for one probe and then wanted again.

## The disposal rule above does NOT apply here

The rehearsal section says the builder archives the scratch repo and the
operator deletes it. **That rule is for drills.** Archiving this repo defeats
its entire purpose, and it is the failure mode the three archived drill repos
demonstrate — each was archived correctly, by the rule, and each then had to be
un-archived or replaced.

So: never archive it, never delete it, and if you find it archived, un-archive
it rather than minting a fourth one.

## Standing it up is the operator's step

Bot identities cannot create repositories in `heavy-duty`. Measured
2026-08-05 with a fleet identity holding the `repo` scope:

```
POST /api/v1/orgs/heavy-duty/repos   ->  403  "not allowed to create repository in organization"
POST /api/v1/user/repos              ->  201  (personal namespace only)
```

This is the same shape as the drill delete: a deliberate permission boundary,
not a misconfiguration. Do not retry it, and do not work around it by putting
the venue in a personal namespace — **not because a personal namespace is
proven unable to reach the org's runner** (that was not measured; the probe
repository above was deleted immediately, so nothing about runner or secret
reach was established), but because @andres ruled an **org-owned standing
venue** (#5631). A personally-owned repo is a different thing from the one that
was decided on, and cannot satisfy #202's named acceptance target.

If runner or secret reach turns out to matter, measure it once the venue
exists rather than assuming it here.

## Running a probe

1. Reset the repo to a clean state — the probe's own fixtures only, no
   leftovers from the last one. A probe that inherits state is a probe whose
   result you cannot attribute.
2. **Arm it against the candidate** (below) — two layers, candidate code and
   armed workflow — if the probe is about ceremony's own machinery rather than
   about a bare API call.
3. **Run it as an Actions job under `${{ github.token }}`.** This is the whole
   point of the venue and the one step that cannot be shortcut. A `curl` from a
   laptop with a PAT answers a different question — see the 204/500 split
   above — and a probe run that way is worse than no probe, because it produces
   a confident wrong answer.
4. **The job writes its raw results into an issue in the PROBE repo** —
   `heavy-duty/ceremony-runner-probe` — not into ceremony. Logs age out;
   ceremony#192's run 701 survived only because the job wrote its findings
   into an issue it created.
5. **A human then records the probe issue's URL and the Actions run number on
   the ceremony issue the probe serves.** That hop is deliberate and is the
   whole of the boundary: the probe workflow holds no credential and no code
   path that can write to `heavy-duty/ceremony`, so "the probe reports its
   findings" and "the probe cannot touch the live board" stay compatible
   rather than contradicting each other (@codex-reviewer-andresmgsl, #202
   review).

## Arming a candidate ref

A probe that exercises ceremony's own machinery needs the candidate tree
reachable from a `uses:` line. This is the fork-ref shape `drills/README.md`
step 2 points at, written out — and it has **two layers**, which is the part
that is easy to get wrong and impossible to fix afterwards.

**Why two.** The candidate's own workflows contain
`repository: heavy-duty/ceremony` beside `ref: ${{ env.CEREMONY_SELF_REF }}`,
so they must be rewritten to point at the fork and at the candidate. But
rewriting them **creates a new commit**, and a commit cannot contain its own
object ID. A single-layer arming is therefore self-referential: pin the callers
to the pre-rewrite SHA and they load the *unarmed* workflows; pin them to the
post-rewrite one and you are asking a commit to embed itself
(@codex-reviewer-andresmgsl, #202 review).

So:

| layer | what it is | what it carries |
|---|---|---|
| **candidate code SHA** | the immutable tree under test | `actions/`, `lib/` — untouched |
| **armed workflow SHA** | a small child commit on top of it | workflows rewritten to the fork + `CEREMONY_SELF_REF` = the candidate code SHA |

### The procedure

1. **Push the candidate tree** to a fork under the identity that will run the
   probe — one branch, `<identity>/ceremony@probe-<issue>` — and record its
   SHA. Steps 1 and 2 advance the tip of that **same** branch; there are two
   commits, not two branches. That is
   the **candidate code SHA**. Never create a branch on
   `heavy-duty/ceremony` named like a tag: it shadows that tag for every
   consumer until somebody remembers to delete it.
2. **Write the manifest FIRST, from the pre-arming tree, then commit the
   arming.** The manifest enumerates the carriers *that must change*, so it is
   generated before they do — running it afterwards would enumerate
   already-rewritten rows and lose the canonical internal-checkout ones
   entirely (@codex-reviewer-andresmgsl, #202 review). In that same
   fork branch rewrite, for **every** carrier the manifest below enumerates:
   ceremony's own internal `repository:` checkouts → `<identity>/ceremony`, and
   **every** `CEREMONY_SELF_REF` value → the **candidate code SHA** from step 1.
   There were three self-ref carriers on `main` at the time of writing and the
   count is not a constant — derive it, do not remember it
   (@glm-reviewer-andresmgsl, @codex-reviewer-andresmgsl, #202 review). The
   **consumer** checkouts (`${{ github.repository }}`) are left alone. Record
   the resulting SHA: that is the **armed workflow SHA**.
3. **Pin the probe repo's callers by layer**, because they are not the same
   thing:
   - composite-action callers →
     `<identity>/ceremony/actions/<name>@<candidate-code-sha>`;
   - reusable-workflow callers →
     `<identity>/ceremony/.github/workflows/<file>@<armed-workflow-sha>`, since
     that is the only revision whose inner checkout is rewritten.
4. **Gate the arming against a MANIFEST, byte for byte.** Every weaker shape
   has a hole, and each of these was found in a published draft of this file
   (@codex-reviewer-andresmgsl, #202 review):

   | weaker check | what slips through |
   |---|---|
   | "the old literal is absent" | a carrier rewritten to the wrong fork, or to the *armed* SHA |
   | "every extracted value equals X" | a carrier that **vanished** — nothing to compare |
   | "each value is one of {fork, dynamic}" | a **role swap**: an internal checkout made dynamic, a consumer checkout pointed at the fork |
   | "the SHA suffix matches" | `wrong-owner/ceremony/actions/foo@<right-sha>` |
   | "known callers match" | an **unrecognised** caller, or none at all |
   | "the owner and the sha are right for the kind" | a **layer swap**: `…/actions/x@<armed>` labelled a workflow caller satisfies both |

   So the arming step **writes a manifest** — one line per carrier, `path`,
   `kind`, `full expected value` — and the gate compares the tree's actual
   carriers against it as a set. A deletion, a role swap, a wrong fork, a wrong
   SHA, an extra carrier and a missing caller are then all the same kind of
   failure: the sets differ.

   **Generate it while arming**, from the tree you are arming, so the manifest
   cannot drift from the repository:

   ```sh
   #!/usr/bin/env bash
   # write-manifest <candidate-checkout> <probe-checkout> <fork> <code-sha> <armed-sha>
   #
   # Run against the PRE-ARMING tree and the UNPINNED probe: this records what
   # each carrier must BECOME, so it has to see them before they change.
   #
   # `|| true` on every extraction, for the same reason the checker needs it:
   # git grep exits 1 on no-match and `set -e` would abort BEFORE the manifest
   # is written — silently, which is how the first version of this generator
   # produced no file and no diagnostic when a probe exercised only one layer
   # (@codex-reviewer-andresmgsl). A probe need not use both.
   set -euo pipefail
   candidate="$1"; probe="$2"; fork="$3"; code_sha="$4"; armed_sha="$5"
   # shellcheck disable=SC2016 # `${{ github.repository }}` is literal YAML, not a shell expansion
   {
     git -C "$candidate" grep -n 'CEREMONY_SELF_REF:' -- .github/workflows \
       | cut -d: -f1,2 | sed "s|$|\tself_ref\t$code_sha|" || true
     git -C "$candidate" grep -n 'repository: heavy-duty/ceremony' -- .github/workflows \
       | cut -d: -f1,2 | sed "s|$|\tinternal_repo\t$fork|" || true
     git -C "$candidate" grep -n 'repository: ${{ github.repository }}' -- .github/workflows \
       | cut -d: -f1,2 | sed 's|$|\tconsumer_repo\t${{ github.repository }}|' || true
     # Callers record the COMPLETE expected coordinate, not just the sha: the
     # path is as rewritable as the owner, and a manifest that stores only the
     # suffix cannot notice `…/actions/wrong-one@<right-sha>`.
     git -C "$probe" grep -nE 'uses:[[:space:]]*[^[:space:]]*/ceremony/\.github/workflows/' -- .github \
       | sed -E "s|^([^:]+):([0-9]+):.*/ceremony/(\.github/workflows/[^@[:space:]]+)@.*|\\1:\\2\\tworkflow_caller\\t$fork/\\3@$armed_sha|" || true
     git -C "$probe" grep -nE 'uses:[[:space:]]*[^[:space:]]*/ceremony/actions/' -- .github \
       | sed -E "s|^([^:]+):([0-9]+):.*/ceremony/(actions/[^@[:space:]]+)@.*|\\1:\\2\\taction_caller\\t$fork/\\3@$code_sha|" || true
   } | sort >manifest.tsv

   # Zero ceremony callers is a refusal by name; one layer only is fine.
   callers="$(grep -cE '(workflow|action)_caller' manifest.tsv || true)"
   [ "$callers" -gt 0 ] || { echo "manifest: no ceremony callers found in $probe" >&2; exit 1; }
   ```

   Then arm — rewrite and commit — and check the result against it:

   ```sh
   #!/usr/bin/env bash
   # check-arming <armed-checkout> <probe-checkout> <fork> <code-sha> <armed-sha> <manifest.tsv>
   set -euo pipefail
   armed="$1"; probe="$2"; fork="$3"; code_sha="$4"; armed_sha="$5"; manifest="$6"
   fail() { echo "arming incomplete: $*" >&2; exit 1; }

   # `|| true` on every extraction: git grep exits 1 when nothing matches, and
   # under `set -e` that would kill this script BEFORE the comparison — so a
   # carrier class that vanished ENTIRELY produced silence instead of a
   # refusal. Silence is the worst of the three outcomes; the comparison below
   # is what must report it.
   [ "$(grep -cE '(workflow|action)_caller' "$manifest" || true)" -gt 0 ] \
     || fail "manifest names no ceremony callers — it cannot prove an arming"

   # THE MANIFEST ITSELF IS CHECKED AGAINST THE TARGET, not trusted. Comparing
   # only tree-vs-manifest proves consistency, and a manifest generated with the
   # armed SHA where the candidate SHA belonged — or with the wrong fork —
   # describes a WRONG arming perfectly. The tree would then match it and the
   # gate would pass (@codex-reviewer-andresmgsl, #202 review).
   # shellcheck disable=SC2016 # `${{ github.repository }}` below is literal YAML
   while IFS=$'\t' read -r loc kind want; do
     case "$kind" in
       self_ref)        [ "$want" = "$code_sha" ] || fail "manifest $loc: self_ref should be the CANDIDATE sha" ;;
       internal_repo)   [ "$want" = "$fork" ]     || fail "manifest $loc: internal repo should be $fork" ;;
       consumer_repo)   [ "$want" = '${{ github.repository }}' ] \
                          || fail "manifest $loc: consumer checkout must stay dynamic" ;;
       # THE KIND MUST BIND TO THE PATH CLASS, not only to the owner and the
       # sha. The path class is what SAYS which layer a caller is, so checking
       # the sha against the kind while letting the kind float free accepts a
       # consistent layer swap — `…/actions/x@<armed>` declared workflow_caller
       # passes every owner and sha test (@codex-reviewer-andresmgsl, #202
       # review). Decompose once, then let the kind fix BOTH coordinates.
       workflow_caller|action_caller)
                        owner="${want%%/ceremony/*}"; rest="${want#*/ceremony/}"
                        path="${rest%@*}"; sha="${want##*@}"
                        [ "$owner/ceremony" = "$fork" ] \
                          || fail "manifest $loc: caller owner should be $fork"
                        case "$kind" in
                          workflow_caller)
                            case "$path" in .github/workflows/?*) : ;;
                              *) fail "manifest $loc: workflow_caller must resolve at .github/workflows/<file>, not '$path'" ;;
                            esac
                            [ "$sha" = "$armed_sha" ] || fail "manifest $loc: workflow caller should be the ARMED sha" ;;
                          action_caller)
                            case "$path" in actions/?*) : ;;
                              *) fail "manifest $loc: action_caller must resolve at actions/<name>, not '$path'" ;;
                            esac
                            [ "$sha" = "$code_sha" ] || fail "manifest $loc: action caller should be the CANDIDATE sha" ;;
                        esac ;;
       *)               fail "manifest $loc: unknown kind '$kind'" ;;
     esac
   done <"$manifest"

   actual="$(mktemp)"; trap 'rm -f "$actual"' EXIT
   {
     git -C "$armed" grep -nP '(?<=CEREMONY_SELF_REF: ")[^"]+' -- .github/workflows \
       | sed -E 's/^([^:]+):([0-9]+):.*CEREMONY_SELF_REF: "([^"]*)".*/\1:\2\tself_ref\t\3/' || true
     git -C "$armed" grep -nE 'repository: .+' -- .github/workflows \
       | sed -E 's|^([^:]+):([0-9]+):[[:space:]]*repository:[[:space:]]*(.*)$|\1:\2\t__repo__\t\3|' || true
     # Only CEREMONY callers, matching the generator's domain exactly — a
     # third-party `actions/checkout` is not this gate's business, and
     # extracting it here while the generator ignores it made every probe fail
     # as an "unrecognised carrier" (@codex-reviewer-andresmgsl). A wrong OWNER
     # is still caught: `wrong-owner/ceremony/...` matches this pattern.
     git -C "$probe" grep -nE 'uses:[[:space:]]*[^[:space:]]*/ceremony/' -- .github \
       | sed -E 's|^([^:]+):([0-9]+):[[:space:]]*-?[[:space:]]*uses:[[:space:]]*(.*)$|\1:\2\t__uses__\t\3|' || true
   } | sort >"$actual"

   # every manifest line must be present with its EXACT expected value, and the
   # kinds must match — a role swap changes the kind, not just the value.
   while IFS=$'\t' read -r loc kind want; do
     case "$kind" in
       self_ref)        have="$(awk -F'\t' -v l="$loc" '$1==l && $2=="self_ref"{print $3}' "$actual")" ;;
       internal_repo|consumer_repo)
                        have="$(awk -F'\t' -v l="$loc" '$1==l && $2=="__repo__"{print $3}' "$actual")" ;;
       workflow_caller|action_caller)
                        have="$(awk -F'\t' -v l="$loc" '$1==l && $2=="__uses__"{print $3}' "$actual")" ;;
     esac
     [ -n "$have" ] || fail "carrier vanished: $loc ($kind)"
     # ONE comparison for every kind: the manifest already carries the complete
     # expected value, so owner, path AND sha are checked at once. Checking the
     # owner and the sha separately let `…/actions/wrong-one@<right-sha>`
     # through (@codex-reviewer-andresmgsl).
     [ "$have" = "$want" ] || fail "$loc ($kind): expected '$want', found '$have'"
   done <"$manifest"

   # and nothing UNRECOGNISED: every uses:/repository: in the trees must appear
   # in the manifest, so an added carrier is a failure rather than a silence.
   while IFS=$'\t' read -r loc _ _; do
     grep -qF "$loc"$'\t' "$manifest" || fail "carrier not in manifest: $loc"
   done <"$actual"
   ```

   **Why a manifest rather than a longer list of assertions.** The carrier set
   is a property of the tree at the moment of arming; any list written into
   this document is stale the next time a workflow is added. The manifest is
   generated from the tree, recorded in the result issue (step 6), and is the
   thing a later reader compares against — so "what was armed" is evidence
   rather than recollection.

5. **Invoke the probe by the event it is about**, and record which: a
   `workflow_dispatch`, or the real board event under test. A probe that fires
   a different event than the one under test proves something else.
6. **The result issue records all of it**: the fork repository, the candidate
   code SHA, the armed workflow SHA, every rewritten carrier, the workflow
   invoked and the run number. Those are what make the result reproducible;
   without the two SHAs distinguished, a later reader cannot tell which tree
   answered.
7. **Reset removes the candidate-specific EXECUTABLE state**: the caller stubs,
   the probe workflow, and the fork's probe branch — whose tip carries both the
   candidate commit and the armed commit on top of it — so the next probe
   cannot inherit a pin it did not choose. **Result issues are never deleted.**
   They may be closed or relabelled; deleting them would recreate the
   expiring-log problem this venue exists to avoid.

## Who may reset it

**Operator-owned until ruled otherwise.** #202's task 4 asks who may reset the
venue, and creating the repo is the operator's step, so the access policy is
his to set at the same time (@codex-reviewer-andresmgsl, #202 review).

Two levels, deliberately separated:

- **content reset** — removing probe branches, workflows and fixtures; the
  ordinary between-probes operation. It does **not** include deleting result
  issues, which are the evidence and are immutable once written
  (@codex-reviewer-andresmgsl, #202 review);
- **archive / delete / admin** — which is where the drill rule's damage came
  from, and which no bot identity should hold here.

If fleet identities are given push access for content reset, this section
records that; until then, ask.

## What must never happen here

No probe touches `heavy-duty/ceremony`'s board. No labels, no comments, no
runs attributable to a probe. The venue exists so that the live board does not
have to be the test fixture.

## The probes this venue owes — and the records of those delivered

Delivered probes stay listed with their record: the venue's value is that a
claim like "the asymmetry reproduces" carries a URL a reader can open, not a
memory.

- **ceremony#192** — DELIVERED, first drill (2026-08-05). Under
  `${{ github.token }}` in the venue:
  `DELETE /issues/{n}/labels/{id}` → **500**, the label still on the issue
  afterward — the failure observable in the set, not merely a status — then
  `PUT` full-set clear → **200**, set actually empty. Record:
  [probe issue #1](https://forgejo.heavyduty.builders/heavy-duty/ceremony-runner-probe/issues/1)
  (run 1) and
  [probe issue #2](https://forgejo.heavyduty.builders/heavy-duty/ceremony-runner-probe/issues/2)
  (run 4 — the clean independent repeat after the redaction incident below).
- **ceremony#205** — DELIVERED with a correction to the line above's
  premise. The dispatch route answers **204** to a valid body carrying the
  bare resolvable ref `main` — under the workflow token
  ([ceremony#205 comment #6262](https://forgejo.heavyduty.builders/heavy-duty/ceremony/issues/205#issuecomment-6262),
  run 504, and again as
  [probe issue #4](https://forgejo.heavyduty.builders/heavy-duty/ceremony-runner-probe/issues/4),
  run 6) and under a PAT
  ([probe issue #5](https://forgejo.heavyduty.builders/heavy-duty/ceremony-runner-probe/issues/5),
  run 7, and ceremony run 459). The earlier opaque `500` came from a bare
  UNRESOLVABLE ref or an unknown/unparseable workflow — the diagnostic !213
  ships now names this; a fully-qualified bad ref gets a clean 404 instead.
  The `GET /actions/workflows` listing still 404s. Claims here are limited to
  what those runs measured.
- **ceremony#215** — the discriminator drill: REST-body `inputs` DO reach a
  top-level dispatched workflow, both contexts
  (`inputs.*` and `github.event.inputs.*`), both identities. What loses the
  value is the `workflow_call` boundary — a called workflow does not see the
  caller's `event.inputs` on this instance. Records:
  [probe issues #4 and #5](https://forgejo.heavyduty.builders/heavy-duty/ceremony-runner-probe/issues/4)
  (runs 6 and 7).
- **ceremony#217** — DELIVERED (2026-08-09). The standing venue used the
  published consumer callers without rewrites or bypasses:
  `labels.yml@0.6.1` and `labels-sweep.yml@0.6.1`. Opening fixture issue #7
  drove event caller
  [run 23](https://forgejo.heavyduty.builders/heavy-duty/ceremony-runner-probe/actions/runs/23)
  and its dispatched sweep
  [run 24](https://forgejo.heavyduty.builders/heavy-duty/ceremony-runner-probe/actions/runs/24);
  the sweep wrote `needs-triage` on that issue under the workflow token. A
  separate manual sweep was green in
  [run 25](https://forgejo.heavyduty.builders/heavy-duty/ceremony-runner-probe/actions/runs/25).
  Observer
  [run 30](https://forgejo.heavyduty.builders/heavy-duty/ceremony-runner-probe/actions/runs/30)
  recorded the released tag SHA `338cf5f754f0e87feefe9231b47910fb236ab4d0`,
  both caller runs and the resulting label set in
  [probe issue #10](https://forgejo.heavyduty.builders/heavy-duty/ceremony-runner-probe/issues/10).
  The event caller loaded its reusable workflow at `@0.6.1`; both sweep runs
  completed the reusable workflow's internal `CEREMONY_SELF_REF` checkout at
  the real `0.6.1` tag. There was no candidate SHA rewrite and no dogfood
  bypass.

Two venue lessons from the first drills, kept where the next probe author will
look:

- **Rule 4 is load-bearing on this instance**: the probe repo's web log route
  404s for non-admin reads, and a log-only observation (run 2) was lost where
  issue-written ones were not.
- **Report content sent to the forge must never contain a credential
  expression OR a credential value** — moving a secret from `${{ … }}` syntax
  into a shell variable does not make it safe to emit. Name identities in
  literal prose ("the workflow token"), allowlist the fields a report emits,
  and treat anything else as unsendable. The incident this teaches from: an
  escaped `${{ github.token }}` in a comment template was expanded by the
  runner into the recorded text (the run's ephemeral token); it was redacted
  in place and the drill repeated clean (probe issue #2, run 4).