diff --git a/docs/cli.md b/docs/cli.md
index e4a7c07..a9c76c7 100644
--- a/docs/cli.md
+++ b/docs/cli.md
@@ -43,7 +43,7 @@ secrets-engine --version
 | `SECRETS_ENGINE_APPROVAL_TOKEN_FILE` | _(unset)_ | explicit approval bearer file; conflicts with approval client-secret provider |
 | `SECRETS_ENGINE_KEYCAPE_TOKEN_URL` | _(unset)_ | KeyCape token endpoint for `service-jwt` |
 | `SECRETS_ENGINE_KEYCAPE_ISSUER` | _(unset)_ | KeyCape issuer; must match the JWT login contract |
-| `SECRETS_ENGINE_KEYCAPE_CLIENT_SECRET_FILE` | _(unset)_ | mode-0600 out-of-repo client secret |
+| `SECRETS_ENGINE_KEYCAPE_CLIENT_SECRET_FILE` | _(unset)_ | **refused** since 2026-10-06: the secrets-engine-openbao secret is read in memory from OpenBao per command (see keycape-openbao-consumer-custody.md) |
 | `SECRETS_ENGINE_OPENBAO_JWT_LOGIN` | _(unset)_ | platform JWT mount/role contract YAML |
 
 ## Commands
diff --git a/docs/keycape-openbao-consumer-custody.md b/docs/keycape-openbao-consumer-custody.md
index 89ea17b..5affaad 100644
--- a/docs/keycape-openbao-consumer-custody.md
+++ b/docs/keycape-openbao-consumer-custody.md
@@ -1,154 +1,114 @@
-# KeyCape `secrets-engine-openbao` consumer custody packet
+# KeyCape `secrets-engine-openbao` client secret: consumer custody
 
-Prepared 2026-10-06 by secrets-engine for KEY-WP-0037-T02 and
-RPF-WP-0035-T02 (proposed CCR-2026-0033 custody child). Tracked in
-SECRETS-WP-0012. **Source and documentation only.** No value was generated,
-fetched or written; no host, cluster, OpenBao or KeyCape state was changed.
-The founder's custody-boundary decision `632a8893-0d6a-4591-a50b-40bbdb798f32`
-approves the two-copy boundary, not generation, fetch, delivery, registration
-or deployment. Each live step below still needs its own approval.
+Rewritten 2026-10-06 by secrets-engine. Tracked in SECRETS-WP-0012.
+**Source and documentation only.** No value was generated, fetched or written;
+no host, cluster, OpenBao or KeyCape state was changed.
 
-This packet names the **consumer copy only**: the secrets-engine-owned
-mode-0600 file. The authoritative copy (platform KV
-`platform/services/keycape/secrets-engine-openbao`, field `CLIENT_SECRET`) and
-the issuer-side ESO copy (`sso` Secret `keycape-secrets-engine-openbao-client`,
-key `client-secret`) are platform's and KeyCape's. Issuer ESO does not supply
-this copy, and nothing here adds a client-side OpenBao reader.
+## Direction
 
-## What the code supports (determined from source)
+Founder direction 2026-10-06: the `secrets-engine-openbao` KeyCape client
+secret lives **only in OpenBao**. There is no persistent workstation copy.
+ops-mason decided placement and the read lane in
+`ops-mason/plans/keycape-secrets-engine-openbao-client-custody.md` (commit
+`658cdbc`, workplan MASON-WP-0009; status *reviewed*, founder approvals A1–A3
+pending). That direction and plan **supersede the earlier consumer-file packet
+and its decisions D1–D4** (host, OS user, persistent file path, rotation
+cadence). The consumer-file custody child in CCR-2026-0033 is out of direction
+and is being revised by railiance-platform.
 
-- secrets-engine is a CLI, not a daemon. The OpenBao JWT login runs inside
-  whichever process an operator starts with `--auth service-jwt` (or `auto`
-  once `SECRETS_ENGINE_OPENBAO_JWT_LOGIN` is set); it logs in for one command
-  and self-revokes (`engine_auth.login_service_jwt`). There is no service
-  account, unit file or container for the engine.
-- The provider reads the secret from the path in
-  `SECRETS_ENGINE_KEYCAPE_CLIENT_SECRET_FILE` (`config.py`), rereads it before
-  every exchange and sends it only as HTTP Basic (`service_auth.py`).
-- As of this packet the read goes through `read_client_secret_file`, which
-  refuses, without exposing the value: a relative path; a missing file; any
-  symlink or non-canonical path component; a non-regular file; a file or
-  parent directory not owned by the effective user; any group/other mode bit on
-  the file (must be 0600) or its parent (must be 0700); a path inside a Git
-  worktree; empty content; content that is not exactly one token. Before this
-  change only the file mode, worktree and empty checks existed. The approval
-  profile shares the same provider and therefore the same checks.
-- `secrets-engine service-auth check-secret-file [--path P] [--json]` runs those
-  checks and prints check names and pass/fail only — never the value, its
-  length or any hash. Exit 0 = accepted, 1 = refused. This is the bounded
-  validation interface RPF-WP-0035-T02 asked for.
+## Coordinates (non-secret)
 
-## Consumer coordinates
+| Item | Value |
+|---|---|
+| Authoritative entry | KV v2 mount `platform`, path `workloads/keycape/secrets-engine-openbao` (API `platform/data/workloads/keycape/secrets-engine-openbao`), field `CLIENT_SECRET` |
+| Issuer copy | `sso` Secret `keycape-secrets-engine-openbao-client` key `client-secret`, via ESO on Kubernetes auth (platform/KeyCape; unchanged) |
+| Consumer copy | **none** — the value exists only in process memory for one command |
+| Consumer read lane | OIDC mount `auth/netkingdom`, role `keycape-secrets-engine-openbao-operator-workload-kv-read`, policy `workload-kv-read-keycape-secrets-engine-openbao-operator` (read on the data path, `update` on `auth/token/revoke-self`, nothing else), 5m TTL, 4 uses, bound `groups=net-kingdom-admins` |
+| Companion config | `BAO_ADDR=https://bao.coulomb.social`, `SECRETS_ENGINE_KEYCAPE_TOKEN_URL=https://kc.coulomb.social/token`, `SECRETS_ENGINE_KEYCAPE_ISSUER=https://kc.coulomb.social`, `SECRETS_ENGINE_OPENBAO_JWT_LOGIN=<platform-published contract file>` |
 
-| Coordinate | Value | Basis |
-| --- | --- | --- |
-| Host | Operator workstation (the WSL2 Linux host where every documented live secrets-engine OpenBao operation runs against `BAO_ADDR=https://bao.coulomb.social`) | Documented practice; **founder decision D1** |
-| OS user / owner | `worsch`, file and parent `worsch:worsch` | The account that runs the CLI; **founder decision D2** |
-| File | `/home/worsch/.secrets-engine/keycape/secrets-engine-openbao.client-secret` | Follows existing `~/.secrets-engine/bootstrap/` convention |
-| File mode | `0600`, regular file, single token, no trailing data other than one newline | Enforced by code |
-| Parent | `/home/worsch/.secrets-engine/keycape`, `0700`, owned by `worsch` | Enforced by code |
-| Grandparent | `/home/worsch/.secrets-engine` exists today as `0755` with only `0700` children; not changed by this packet | Observed metadata only |
-| Git | Outside every worktree (`/home/worsch` and `~/.secrets-engine` are not worktrees) | Enforced by code |
-| Storage | Persistent ext4 home, not tmpfs | **Founder decision D3** |
-| Config reference | `SECRETS_ENGINE_KEYCAPE_CLIENT_SECRET_FILE=<file above>` | `config.py` |
-| Companion config | `SECRETS_ENGINE_KEYCAPE_TOKEN_URL=https://kc.coulomb.social/token`, `SECRETS_ENGINE_KEYCAPE_ISSUER=https://kc.coulomb.social`, `SECRETS_ENGINE_OPENBAO_JWT_LOGIN=/home/worsch/.secrets-engine/keycape/openbao-jwt-login.yaml` (non-secret `mount`/`role: secrets-engine-openbao`/`bound_issuer`, content published by platform) | `engine_auth.py`, platform design |
+The mount, path, field and role are pinned in
+`service_auth.OpenBaoOidcClientSecretSource`; any other value is refused.
 
-One host and one file. A second host or user would be a third copy and needs
-its own approval; the engine has no mechanism that distributes the file.
+## What the code does (per command that selects `service-jwt`)
 
-## Delivery (platform custody → this file)
+1. Runs `bao login -method=oidc -path=netkingdom -no-store -format=json
+   role=keycape-secrets-engine-openbao-operator-workload-kv-read`. The
+   browser/MFA prompt goes to the operator's terminal (stderr); the login
+   response is captured from a **stdout pipe into memory**. `BAO_TOKEN` and
+   `VAULT_TOKEN` are removed from the child environment, and `-no-store` keeps
+   the token out of the token helper. For non-token methods the CLI does not
+   send a helper-stored token. The token never appears in argv, env, a file,
+   a log or evidence.
+2. One in-process HTTPS `GET /v1/platform/data/workloads/keycape/secrets-engine-openbao`
+   with the token only in the `X-Vault-Token` header; extracts `CLIENT_SECRET`
+   (must be exactly one non-empty token).
+3. `POST /v1/auth/token/revoke-self` with the same token — always, also when
+   the read fails.
+4. The value goes in memory to the KeyCape `/token` `client_credentials`
+   exchange (HTTP Basic only), then the existing OpenBao JWT login on the
+   platform role and its self-revoke at command end. The value is dropped
+   when the exchange request is built.
 
-Attended operator path, executed on the host above as `worsch`, inside the
-platform-owned custody child of CCR-2026-0033:
+Refusals: `SECRETS_ENGINE_KEYCAPE_CLIENT_SECRET_FILE` set → refused for this
+profile; a `KeyCapeServiceAuthConfig` with a file → refused; a provider for this
+profile without the in-memory source → refused. `service-jwt` still never falls
+back to `--bootstrap-token-file`, `BAO_TOKEN` or AppRole. The approval client
+(`secrets-engine-approval`) keeps its own file source and
+`service-auth check-secret-file` for it.
 
-1. Preconditions: founder approval of the exact custody child; platform's
-   operator OpenBao session for the KV write; `umask 077`; shell tracing and
-   credential-bearing debug logs off.
-2. The custody child generates one random value **in process memory** and
-   compare-before-writes it to the authoritative KV field. If that write fails,
-   no consumer file is written.
-3. In the **same process**, it writes the consumer copy: create the parent
-   with `0700` if absent (refuse if it exists with other owner/mode); open a
-   new temp file in that directory with `O_CREAT|O_EXCL|O_WRONLY`, mode `0600`;
-   write, `fsync`, `rename` onto the final path; `fsync` the directory. The
-   value never appears in argv, environment, stdout/stderr, logs, Git or the hub.
-4. It then runs `secrets-engine service-auth check-secret-file --json` and
-   records only that result plus non-secret IDs in the native receipt.
+Evidence is value-free: `secret_source=openbao-oidc-in-memory`, the operator
+and engine accessor fingerprints (12 hex chars of SHA-256), and both
+revoke-self results. Tests with synthetic values:
+`tests/test_openbao_secret_source.py`.
 
-No client-side read of OpenBao is used or required: the consumer copy is
-written from the same in-memory value that creates the authoritative version.
-If the founder rejects same-process delivery, the only alternative is a
-separately admitted, single-path client-side reader (as RPF-WP-0035-T06 does
-for the approval client); this packet does not request one.
+## First live use (founder-run, attended)
 
-Ownership: platform owns generation, the authoritative write and the delivery
-code path; secrets-engine owns these destination coordinates, the acceptance
-check and the file's lifecycle on the host.
+Run only after **all** of: founder approval of the ops-mason plan (A1), the
+revised CCR-2026-0033 applied by railiance-platform (A2/A3: KV entry written,
+operator OIDC role and policy, ESO reader, JWT role), the KeyCape
+`secrets-engine-openbao` registration live and KeyCape restarted after the KV
+write (KEY-WP-0037), and the platform JWT login contract file published. This
+is the evidence step for KEY-WP-0037-T04 / RPF-WP-0035-T02 and plan
+verification item 6.
 
-## Detecting a failed delivery
+```bash
+cd /home/worsch/secrets-engine && \
+env -u BAO_TOKEN -u VAULT_TOKEN -u SECRETS_ENGINE_KEYCAPE_CLIENT_SECRET_FILE \
+  BAO_ADDR=https://bao.coulomb.social \
+  SECRETS_ENGINE_KEYCAPE_TOKEN_URL=https://kc.coulomb.social/token \
+  SECRETS_ENGINE_KEYCAPE_ISSUER=https://kc.coulomb.social \
+  SECRETS_ENGINE_OPENBAO_JWT_LOGIN=/home/worsch/.secrets-engine/keycape/openbao-jwt-login.yaml \
+  uv run secrets-engine service-auth probe-openbao --json
+```
 
-- `check-secret-file` exits 1 and names the failing check (missing, mode,
-  owner, parent, symlink, worktree, empty). The receipt must carry `ok: true`.
-- At use time the same checks refuse the exchange with `ProvisioningError`
-  (exit 6); `service-jwt` never falls back to bootstrap, `BAO_TOKEN` or AppRole.
-- A value that is well-formed but does not match the issuer is detectable only
-  by the first live exchange (KEY-WP-0037-T04): KeyCape answers HTTP 401 and
-  the engine reports `KeyCape token exchange failed with HTTP 401`. No hash or
-  fingerprint of the value is recorded to compare copies; that is deliberate.
-- Crash between the KV write and the rename: the KV version exists and the
-  consumer file does not (or a stale temp file remains in the 0700 directory).
-  Recovery is a fresh rotation, not a KV read; the operator removes the exact
-  temp file after inspecting its name and metadata only.
+A browser opens for the KeyCape login with MFA (an existing session is
+reused); stderr shows the `bao` OIDC prompt. Expected stdout, exit 0 — one
+line, only these keys, `<fp>` being 12 hex characters:
 
-## Rotation and revocation
+```json
+{"auth_provider": "service-jwt", "established": true, "ok": true, "operator_revocation_attempted": true, "operator_revocation_succeeded": true, "operator_session_handle": "<fp>", "revocation_attempted": true, "revocation_succeeded": true, "secret_source": "openbao-oidc-in-memory", "session_handle": "<fp>"}
+```
 
-| Event | Owner | Action |
-| --- | --- | --- |
-| Generation / authoritative version | railiance-platform | New KV version via the custody child |
-| Issuer pickup | KeyCape / NetKingdom | ESO refresh plus KeyCape restart (secrets load at startup) |
-| Consumer copy replacement | secrets-engine (file), executed in platform's attended child | Atomic rename as above, then `check-secret-file` |
-| Disable on compromise | KeyCape / NetKingdom | Remove or disable the registration first |
-| Retire versions | railiance-platform | Destroy/retire per CCR |
-| Remove consumer copy | secrets-engine operator | See rollback below |
+Anything else is a failure to record, not to retry blindly: exit 1 with
+`error: ...` on stderr names the failed step (OIDC login exit code, KV HTTP
+status, KeyCape HTTP status, JWT login) and, for a source failure, both
+operator revoke flags. `ok: false` means a revoke-self did not succeed; the
+token stays TTL/use-bound (5m/4 uses, engine token per platform role). Record
+the JSON line only; never a value, token or full accessor.
 
-KeyCape holds one secret per client, so rotation has a cutover window: hold
-the new value in the attended process, replace the consumer file only after
-the issuer reload is confirmed, and accept that exchanges fail closed (401) in
-between. Already-issued JWTs live at most 15 minutes; OpenBao tokens from this
-login are self-revoked per command and bounded by platform's TTL/use limits.
-No instant JWT recall is claimed.
+## Rotation, revocation, rollback
 
-Rotation cadence is **founder decision D4**.
-
-## Rollback and cleanup
-
-1. Unset `SECRETS_ENGINE_KEYCAPE_CLIENT_SECRET_FILE` (and the JWT login
-   contract variable) in the operator environment.
-2. Remove the exact file path (no recursive removal); `rmdir` the parent only
-   if it is empty.
-3. Verify with `check-secret-file --path <file>`: it must exit 1 on `exists`.
-4. Record cleanup status only. Unlink on ext4 is not secure erasure and not
-   revocation; revocation is the KeyCape and platform steps above.
-
-## Founder / owner decisions (with recommendation)
-
-- **D1 Host.** Recommended: the operator workstation only. Alternative:
-  railiance01, which has no documented secrets-engine OpenBao operator use and
-  would need its own user and path decision.
-- **D2 OS user.** Recommended: the operator account `worsch`, since the engine
-  runs only as that user's CLI. A dedicated system user only makes sense once
-  an unattended engine runtime exists, and no source supports one today.
-- **D3 Persistence.** Recommended: persistent home storage. tmpfs would
-  require re-delivery after every reboot, and every re-delivery would need either
-  a rotation or an unadmitted client-side KV read. Open owner question: whether
-  any workstation backup or sync tool covers `~/.secrets-engine`. If one does,
-  exclude it there before delivery.
-- **D4 Rotation cadence.** Recommended: event-driven (compromise, host or user
-  change, operator departure) plus a 90-day scheduled rotation run through the
-  same attended child. Platform's CCR sets the binding value.
+Platform-owned (plan §3.5): roll-forward KV writes with `cas=<current>`,
+event-driven plus 90 days, then KeyCape restart. The consumer needs no action:
+the next command reads the latest version. Exchanges fail closed (401) between
+the KV write and the KeyCape restart. On compromise KeyCape/NetKingdom disable
+the registration first. secrets-engine can neither write nor rotate this entry
+and never reads an old version.
 
 ## Not established
 
-No registration, issued JWT, KV version, ESO Secret or consumer file exists
-by implication of this packet. Code tests use synthetic values only and prove
-file acceptance/refusal, not live delivery, issuer match or OpenBao login.
+No live OIDC login, KV read, revoke-self, KeyCape exchange or JWT login has
+run. The operator role, policy, KV entry and JWT contract file do not exist
+yet as far as this repository knows. `bao login -no-store -format=json`
+output shape for OIDC is taken from the CLI contract and is first exercised by
+the founder run above.
diff --git a/docs/service-auth.md b/docs/service-auth.md
index f730d57..599a1c8 100644
--- a/docs/service-auth.md
+++ b/docs/service-auth.md
@@ -12,17 +12,21 @@ the non-cryptographic contract before any future OpenBao login:
   and renewal when no more than three minutes remain;
 - no ID token, refresh token, implicit retry provider, or fallback identity.
 
-The confidential-client secret must be an explicitly selected mode-0600 file
-outside every Git worktree. It is sent with HTTP Basic authentication and never
-placed in a request body, command argument, evidence record, or object
-representation.
-
-Since 2026-10-06 the file must also be a canonical regular file (no symlink
-component) owned by the running user, in a parent directory owned by that
-user with mode 0700, and hold exactly one token.
-`secrets-engine service-auth check-secret-file [--path P] [--json]` reports
-those checks without the value. Consumer host, path, delivery and lifecycle
-coordinates: [keycape-openbao-consumer-custody.md](keycape-openbao-consumer-custody.md).
+Since 2026-10-06 (founder direction; ops-mason plan
+`keycape-secrets-engine-openbao-client-custody`) the `secrets-engine-openbao`
+client secret has **no consumer file**. Each command that selects
+`service-jwt` reads it in memory from OpenBao (`platform/workloads/keycape/secrets-engine-openbao`,
+field `CLIENT_SECRET`) through one attended `bao login -method=oidc -no-store`
+on role `keycape-secrets-engine-openbao-operator-workload-kv-read`, with the
+token captured from a pipe, used only in a request header, and revoked with
+`revoke-self` right after the read. Ambient `BAO_TOKEN`/`VAULT_TOKEN` and the
+token helper are never used, and `SECRETS_ENGINE_KEYCAPE_CLIENT_SECRET_FILE`
+is refused for this profile. The value is sent only with HTTP Basic
+authentication and never placed in a request body, command argument, env,
+file, evidence record, or object representation.
+`secrets-engine service-auth probe-openbao [--json]` runs the whole chain and
+prints value-free evidence. Coordinates, first-use command and lifecycle:
+[keycape-openbao-consumer-custody.md](keycape-openbao-consumer-custody.md).
 
 JWT payload parsing does not prove a signature. OpenBao must verify RS256
 against the configured issuer before issuing a token. railiance-platform owns
@@ -42,7 +46,8 @@ Canonical provider contract:
 ## Approval identity is separate
 
 [Approval service authentication](approval-service-auth.md) uses its own
-client-secret input, resource audience, exact tenant:platform and per-request
+client-secret file (`SECRETS_ENGINE_APPROVAL_CLIENT_SECRET_FILE`, checked by
+`service-auth check-secret-file`), resource audience, exact tenant:platform and per-request
 read/consume scopes. Never put that credential into the OpenBao provider.
 Both providers now validate KeyCape’s actual `level`/`methods` assurance shape;
 the old `aal`/`method` fixture was incompatible with the issuer.
diff --git a/src/secrets_engine/cli.py b/src/secrets_engine/cli.py
index d491d5e..e46cee2 100644
--- a/src/secrets_engine/cli.py
+++ b/src/secrets_engine/cli.py
@@ -41,7 +41,7 @@ from secrets_engine.approval_consume import (
 from secrets_engine.catalog import get_entry, load_catalog
 from secrets_engine.config import Config, repo_root
 from secrets_engine.decisions import require_approved, resolve_decision
-from secrets_engine.errors import DecisionError, SecretsEngineError
+from secrets_engine.errors import BackendError, DecisionError, SecretsEngineError
 from secrets_engine.evidence import EvidenceWriter, PrivilegedActionEvidence
 from secrets_engine.engine_auth import login_service_jwt, select_engine_auth
 from secrets_engine.lane_state import (
@@ -172,6 +172,8 @@ def _open_backend(cfg: Config, args, evidence: PrivilegedActionEvidence | None =
         try:
             if evidence is not None:
                 evidence.detail["auth_session_handle"] = session.accessor_fingerprint
+                for key, value in session.source_evidence.items():
+                    evidence.detail[f"auth_{key}"] = value
             yield session.client
         finally:
             try:
@@ -957,18 +959,46 @@ def cmd_evidence_classify(cfg: Config, args) -> int:
 # -- parser ----------------------------------------------------------------
 
 
+def cmd_service_auth_probe_openbao(cfg: Config, args) -> int:
+    """First-use proof for the secrets-engine-openbao profile. Value-free."""
+    import json as _json
+
+    try:
+        session = login_service_jwt(cfg)
+    except BackendError as exc:
+        print(f"error: {exc}", file=sys.stderr)
+        return 1
+    try:
+        session.close()
+    except BackendError:
+        pass
+    payload = {"auth_provider": "service-jwt", **session.evidence()}
+    ok = bool(
+        payload.get("operator_revocation_succeeded") and payload.get("revocation_succeeded")
+    )
+    payload["ok"] = ok
+    if args.json:
+        print(_json.dumps(payload, sort_keys=True))
+    else:
+        for key in sorted(payload):
+            print(f"{key}: {payload[key]}")
+    return 0 if ok else 1
+
+
 def cmd_service_auth_check_secret_file(cfg: Config, args) -> int:
     """Value-free acceptance check of the KeyCape consumer secret file."""
     import json as _json
 
     from secrets_engine.service_auth import check_client_secret_file
 
+    # The secrets-engine-openbao profile has no consumer file (founder
+    # direction 2026-10-06); this check serves the approval-client file.
     raw = args.path or (
-        str(cfg.keycape_client_secret_file) if cfg.keycape_client_secret_file else ""
+        str(cfg.approval_client_secret_file) if cfg.approval_client_secret_file else ""
     )
     if not raw:
         print(
-            "error: no path; pass --path or set SECRETS_ENGINE_KEYCAPE_CLIENT_SECRET_FILE",
+            "error: no path; pass --path or set SECRETS_ENGINE_APPROVAL_CLIENT_SECRET_FILE",
             file=sys.stderr,
         )
         return 2
@@ -1218,6 +1248,14 @@ def build_parser() -> argparse.ArgumentParser:
     sacheck.add_argument("--json", action="store_true")
     sacheck.set_defaults(func=cmd_service_auth_check_secret_file)
 
+    saprobe = sasub.add_parser(
+        "probe-openbao",
+        help="attended in-memory secret read, KeyCape exchange and OpenBao JWT "
+        "login, then self-revoke; prints value-free evidence only",
+    )
+    saprobe.add_argument("--json", action="store_true")
+    saprobe.set_defaults(func=cmd_service_auth_probe_openbao)
+
     return p
 
 
diff --git a/src/secrets_engine/engine_auth.py b/src/secrets_engine/engine_auth.py
index 77cc034..7011457 100644
--- a/src/secrets_engine/engine_auth.py
+++ b/src/secrets_engine/engine_auth.py
@@ -16,7 +16,11 @@ import yaml
 
 from secrets_engine.errors import BackendError
 from secrets_engine.openbao import OpenBaoClient, ScopedTokenSession
-from secrets_engine.service_auth import KeyCapeServiceAuthConfig, KeyCapeServiceAuthProvider
+from secrets_engine.service_auth import (
+    KeyCapeServiceAuthConfig,
+    KeyCapeServiceAuthProvider,
+    OpenBaoOidcClientSecretSource,
+)
 
 _NAME_RE = re.compile(r"^[A-Za-z0-9._-]+$")
 PROVIDERS = ("auto", "service-jwt", "bootstrap", "env")
@@ -79,15 +83,22 @@ def load_jwt_login_contract(cfg: Any) -> JwtLoginContract:
 def keycape_config(cfg: Any) -> KeyCapeServiceAuthConfig:
     token_url = str(getattr(cfg, "keycape_token_url", "") or "")
     issuer = str(getattr(cfg, "keycape_issuer", "") or "")
-    secret = _optional_path(getattr(cfg, "keycape_client_secret_file", None))
-    if not token_url or not issuer or secret is None:
+    if _optional_path(getattr(cfg, "keycape_client_secret_file", None)) is not None:
         raise BackendError(
-            "service-jwt requires KeyCape token URL, issuer, and client-secret file"
+            "SECRETS_ENGINE_KEYCAPE_CLIENT_SECRET_FILE is refused for the "
+            "secrets-engine-openbao profile; the secret is read in memory from OpenBao"
         )
-    return KeyCapeServiceAuthConfig(
-        token_url=token_url,
-        issuer=issuer,
-        client_secret_file=secret,
+    if not token_url or not issuer:
+        raise BackendError("service-jwt requires KeyCape token URL and issuer")
+    return KeyCapeServiceAuthConfig(token_url=token_url, issuer=issuer)
+
+
+def _source_note(source: OpenBaoOidcClientSecretSource) -> str:
+    ev = source.evidence()
+    return (
+        f"secret_source={ev['secret_source']} "
+        f"operator_revocation_attempted={ev['operator_revocation_attempted']} "
+        f"operator_revocation_succeeded={ev['operator_revocation_succeeded']}"
     )
 
 
@@ -129,11 +140,19 @@ def login_service_jwt(cfg: Any) -> ScopedTokenSession:
     kcfg = keycape_config(cfg)
     if contract.bound_issuer != kcfg.issuer:
         raise BackendError("OpenBao JWT login issuer does not match KeyCape issuer")
-    service_jwt = KeyCapeServiceAuthProvider(kcfg).exchange()
+    source = OpenBaoOidcClientSecretSource(
+        bao_addr=cfg.bao_addr, bao_bin=shutil.which("bao") or ""
+    )
+    try:
+        service_jwt = KeyCapeServiceAuthProvider(kcfg, secret_source=source).exchange()
+    except BackendError as exc:
+        raise BackendError(f"{exc} [{_source_note(source)}]") from exc
     bao_bin = shutil.which("bao") or shutil.which("vault") or ""
     anon = OpenBaoClient(addr=cfg.bao_addr, token="", bao_bin=bao_bin)
     try:
-        return anon.login_jwt(contract.mount, contract.role, service_jwt.token)
+        session = anon.login_jwt(contract.mount, contract.role, service_jwt.token)
+        session.source_evidence = source.evidence()
+        return session
     finally:
         # Drop the KeyCape JWT from this frame; OpenBao verifies the signature.
         del service_jwt
diff --git a/src/secrets_engine/openbao.py b/src/secrets_engine/openbao.py
index 75e8555..3759300 100644
--- a/src/secrets_engine/openbao.py
+++ b/src/secrets_engine/openbao.py
@@ -88,10 +88,13 @@ class ScopedTokenSession:
     closed: bool = False
     revocation_attempted: bool = False
     revocation_succeeded: bool = False
+    # Value-free evidence of the in-memory client-secret read, if any.
+    source_evidence: dict[str, object] = field(default_factory=dict)
 
     def evidence(self) -> dict[str, object]:
         """Return non-secret lifecycle evidence for this issued session."""
         return {
+            **self.source_evidence,
             "session_handle": self.accessor_fingerprint,
             "established": True,
             "revocation_attempted": self.revocation_attempted,
diff --git a/src/secrets_engine/service_auth.py b/src/secrets_engine/service_auth.py
index 7306026..29225e8 100644
--- a/src/secrets_engine/service_auth.py
+++ b/src/secrets_engine/service_auth.py
@@ -10,14 +10,17 @@ from __future__ import annotations
 import base64
 import binascii
 import json
+import hashlib
+import ipaddress
 import os
 import stat
+import subprocess
 from dataclasses import dataclass, field
 from datetime import datetime, timezone
 from pathlib import Path
 from typing import Any, Callable
 from urllib.error import HTTPError, URLError
-from urllib.parse import urlencode
+from urllib.parse import urlencode, urlsplit
 from urllib.request import Request, urlopen
 
 from secrets_engine.errors import BackendError, ProvisioningError
@@ -37,7 +40,10 @@ RENEW_WINDOW_SECONDS = 3 * 60
 class KeyCapeServiceAuthConfig:
     token_url: str
     issuer: str
-    client_secret_file: Path
+    # The OpenBao profile takes no file: its secret is read in memory from
+    # OpenBao per command (OpenBaoOidcClientSecretSource). The approval
+    # profile subclass still uses a consumer file.
+    client_secret_file: Path | None = None
     client_id: str = CLIENT_ID
     subject: str = SUBJECT
     audience: str = CLIENT_ID
@@ -63,6 +69,11 @@ class KeyCapeServiceAuthConfig:
             raise BackendError("KeyCape service identity claims must match accepted contract")
         if self.timeout_seconds <= 0:
             raise BackendError("KeyCape timeout must be positive")
+        if type(self) is KeyCapeServiceAuthConfig and self.client_secret_file is not None:
+            raise BackendError(
+                "secrets-engine-openbao client secret file source is refused; "
+                "the secret is read in memory from OpenBao per command"
+            )
 
 
 @dataclass(frozen=True)
@@ -238,13 +249,25 @@ def read_client_secret_file(path: Path, *, purpose: str = "KeyCape client secret
 class KeyCapeServiceAuthProvider:
     config: KeyCapeServiceAuthConfig
     transport: Transport = field(default=urlopen, repr=False, compare=False)
+    # In-memory secret source. Required for the OpenBao profile; the approval
+    # profile reads its consumer file when this is None.
+    secret_source: Callable[[], str] | None = field(default=None, repr=False, compare=False)
 
     def exchange(self, *, now: datetime | None = None) -> ServiceJWT:
         """Perform one client-credentials exchange; never retry or fall back."""
-        secret = read_client_secret_file(self.config.client_secret_file)
+        if self.secret_source is not None:
+            secret = self.secret_source()
+        elif type(self.config) is KeyCapeServiceAuthConfig or self.config.client_secret_file is None:
+            raise BackendError(
+                "secrets-engine-openbao requires the in-memory OpenBao secret source; "
+                "no file fallback"
+            )
+        else:
+            secret = read_client_secret_file(self.config.client_secret_file)
         basic = base64.b64encode(
             f"{self.config.client_id}:{secret}".encode("utf-8")
         ).decode("ascii")
+        del secret
         body = urlencode(
             {"grant_type": "client_credentials", "scope": self.config.scope}
         ).encode("ascii")
@@ -292,3 +315,182 @@ class KeyCapeServiceAuthProvider:
         ):
             raise BackendError("KeyCape token response lifetime is outside contract")
         return preflight_service_jwt(token, self.config, now=now)
+
+
+# -- in-memory OpenBao source for the secrets-engine-openbao profile ---------
+#
+# ops-mason plan keycape-secrets-engine-openbao-client-custody (658cdbc),
+# founder direction 2026-10-06: the value lives only in OpenBao. Per command an
+# attended OIDC login on one narrow role yields a 5m/4-use operator token that
+# is captured from a pipe, used once in a request header for the KV GET, and
+# revoked with revoke-self. Nothing is written to file, env, argv or cache.
+
+OIDC_MOUNT = "netkingdom"
+OIDC_ROLE = "keycape-secrets-engine-openbao-operator-workload-kv-read"
+KV_MOUNT = "platform"
+KV_PATH = "workloads/keycape/secrets-engine-openbao"
+KV_FIELD = "CLIENT_SECRET"
+SOURCE_NAME = "openbao-oidc-in-memory"
+_AMBIENT_TOKEN_ENV = ("BAO_TOKEN", "VAULT_TOKEN")
+_MAX_KV_RESPONSE = 65536
+
+Runner = Callable[[list[str], dict[str, str]], "tuple[int, bytes]"]
+
+
+def _run_login(argv: list[str], env: dict[str, str]) -> tuple[int, bytes]:
+    """Run the attended login. stdout is a pipe into memory; stderr (the
+    browser prompt, no token) stays on the operator's terminal."""
+    proc = subprocess.run(  # noqa: S603 - fixed argv, no shell
+        argv,
+        env=env,
+        stdin=subprocess.DEVNULL,
+        stdout=subprocess.PIPE,
+        stderr=None,
+        check=False,
+    )
+    return proc.returncode, proc.stdout
+
+
+def _require_bao_address(addr: str) -> str:
+    try:
+        parts = urlsplit(addr)
+        host = parts.hostname or ""
+        port_ok = parts.port != 0
+    except ValueError:
+        raise BackendError("OpenBao address is invalid for the in-memory secret read") from None
+    if not host or parts.username or parts.password or not port_ok:
+        raise BackendError("OpenBao address is invalid for the in-memory secret read")
+    try:
+        loopback = ipaddress.ip_address(host).is_loopback
+    except ValueError:
+        loopback = host == "localhost"
+    if parts.scheme == "https" or (parts.scheme == "http" and loopback):
+        return addr.rstrip("/")
+    raise BackendError("OpenBao address must be HTTPS or a literal loopback forward")
+
+
+@dataclass
+class OpenBaoOidcClientSecretSource:
+    """Read CLIENT_SECRET in memory through one attended OIDC operator login.
+
+    Evidence is value-free: source name, operator accessor fingerprint, and
+    whether revoke-self was attempted and succeeded.
+    """
+
+    bao_addr: str
+    bao_bin: str = "bao"
+    oidc_mount: str = OIDC_MOUNT
+    oidc_role: str = OIDC_ROLE
+    kv_mount: str = KV_MOUNT
+    kv_path: str = KV_PATH
+    kv_field: str = KV_FIELD
+    timeout_seconds: float = 10.0
+    runner: Runner = field(default=_run_login, repr=False, compare=False)
+    transport: Transport = field(default=urlopen, repr=False, compare=False)
+    accessor_fingerprint: str = ""
+    revocation_attempted: bool = False
+    revocation_succeeded: bool = False
+
+    def __post_init__(self) -> None:
+        pinned = (OIDC_MOUNT, OIDC_ROLE, KV_MOUNT, KV_PATH, KV_FIELD)
+        if (self.oidc_mount, self.oidc_role, self.kv_mount, self.kv_path, self.kv_field) != pinned:
+            raise BackendError("OpenBao secret source coordinates do not match the reviewed plan")
+        self.bao_addr = _require_bao_address(self.bao_addr)
+        if not self.bao_bin:
+            raise BackendError("bao CLI is required for the attended OIDC login")
+
+    def evidence(self) -> dict[str, object]:
+        return {
+            "secret_source": SOURCE_NAME,
+            "operator_session_handle": self.accessor_fingerprint,
+            "operator_revocation_attempted": self.revocation_attempted,
+            "operator_revocation_succeeded": self.revocation_succeeded,
+        }
+
+    def argv(self) -> list[str]:
+        # Token never appears here; -no-store keeps it out of the token helper.
+        return [
+            self.bao_bin,
+            "login",
+            "-method=oidc",
+            f"-path={self.oidc_mount}",
+            "-no-store",
+            "-format=json",
+            f"role={self.oidc_role}",
+        ]
+
+    def _login_env(self) -> dict[str, str]:
+        env = {k: v for k, v in os.environ.items() if k not in _AMBIENT_TOKEN_ENV}
+        env["BAO_ADDR"] = self.bao_addr
+        env.pop("VAULT_ADDR", None)
+        return env
+
+    def _login(self) -> str:
+        code, out = self.runner(self.argv(), self._login_env())
+        try:
+            if code != 0:
+                raise BackendError(f"attended OpenBao OIDC login failed (exit {code})")
+            try:
+                auth = json.loads(out)["auth"]
+                token = str(auth["client_token"])
+                accessor = str(auth.get("accessor", ""))
+            except (UnicodeDecodeError, json.JSONDecodeError, KeyError, TypeError) as e:
+                raise BackendError("malformed OpenBao OIDC login response") from e
+        finally:
+            del out
+        if not token or any(ch.isspace() for ch in token):
+            raise BackendError("OpenBao OIDC login returned no usable token")
+        self.accessor_fingerprint = (
+            hashlib.sha256(accessor.encode("utf-8")).hexdigest()[:12] if accessor else ""
+        )
+        return token
+
+    def _call(self, method: str, path: str, token: str) -> tuple[int, bytes]:
+        request = Request(
+            f"{self.bao_addr}/v1/{path}",
+            data=b"" if method == "POST" else None,
+            method=method,
+            headers={"X-Vault-Token": token, "Accept": "application/json"},
+        )
+        try:
+            response = self.transport(request, timeout=self.timeout_seconds)
+            with response:
+                status = getattr(response, "status", 200)
+                raw = response.read(_MAX_KV_RESPONSE + 1)
+        except HTTPError as e:
+            return e.code, b""
+        except (URLError, TimeoutError, OSError) as e:
+            raise BackendError(f"OpenBao request failed: {method} {path}") from e
+        if len(raw) > _MAX_KV_RESPONSE:
+            raise BackendError("OpenBao response exceeds size bound")
+        return status, raw
+
+    def _read_field(self, token: str) -> str:
+        status, raw = self._call("GET", f"{self.kv_mount}/data/{self.kv_path}", token)
+        if status != 200:
+            raise BackendError(f"OpenBao KV read of the client secret failed with HTTP {status}")
+        try:
+            value = json.loads(raw)["data"]["data"][self.kv_field]
+        except (UnicodeDecodeError, json.JSONDecodeError, KeyError, TypeError) as e:
+            raise BackendError("OpenBao KV response has no client-secret field") from e
+        finally:
+            del raw
+        if not isinstance(value, str) or not value or any(ch.isspace() for ch in value):
+            raise BackendError("OpenBao client-secret field must hold exactly one token")
+        return value
+
+    def _revoke_self(self, token: str) -> None:
+        self.revocation_attempted = True
+        try:
+            status, _ = self._call("POST", "auth/token/revoke-self", token)
+        except BackendError:
+            return
+        self.revocation_succeeded = status in (200, 204)
+
+    def __call__(self) -> str:
+        token = self._login()
+        try:
+            return self._read_field(token)
+        finally:
+            self._revoke_self(token)
+            del token
diff --git a/tests/test_consumer_secret_file.py b/tests/test_consumer_secret_file.py
index 62bc8cd..da692ac 100644
--- a/tests/test_consumer_secret_file.py
+++ b/tests/test_consumer_secret_file.py
@@ -108,6 +108,6 @@ def test_cli_check_reports_without_value(tmp_path, capsys):
 
 def test_cli_check_uses_configured_env_path(tmp_path, capsys, monkeypatch):
     f = _private_file(tmp_path)
-    monkeypatch.setenv("SECRETS_ENGINE_KEYCAPE_CLIENT_SECRET_FILE", str(f))
+    monkeypatch.setenv("SECRETS_ENGINE_APPROVAL_CLIENT_SECRET_FILE", str(f))
     assert cli.main(["service-auth", "check-secret-file"]) == 0
     assert "accepted" in capsys.readouterr().out
diff --git a/tests/test_engine_auth.py b/tests/test_engine_auth.py
index a59977d..71f2535 100644
--- a/tests/test_engine_auth.py
+++ b/tests/test_engine_auth.py
@@ -80,15 +80,11 @@ def test_explicit_service_jwt_fails_closed_without_contract(tmp_path, monkeypatc
 
 def test_jwt_login_failure_does_not_fall_back_to_env(tmp_path, monkeypatch):
     monkeypatch.setenv("BAO_TOKEN", "must-not-be-used")
-    secret = tmp_path / "client.secret"
-    secret.write_text("client-secret-value", encoding="utf-8")
-    secret.chmod(0o600)
     cfg = _cfg(
         tmp_path,
         openbao_jwt_login_file=_jwt_contract(tmp_path),
         keycape_token_url="https://keycape.example.test/token",
         keycape_issuer="https://keycape.example.test",
-        keycape_client_secret_file=secret,
     )
     monkeypatch.setattr(
         "secrets_engine.engine_auth.KeyCapeServiceAuthProvider.exchange",
diff --git a/tests/test_openbao_secret_source.py b/tests/test_openbao_secret_source.py
new file mode 100644
index 0000000..d0f9342
--- /dev/null
+++ b/tests/test_openbao_secret_source.py
@@ -0,0 +1,236 @@
+"""In-memory OpenBao source for the secrets-engine-openbao client secret.
+
+Synthetic values only. Proves the operator token and the client secret never
+reach argv, env, stdout/stderr or files, that revoke-self always runs, and that
+the file source and ambient tokens are refused for this profile.
+"""
+import functools
+import json
+import os
+from types import SimpleNamespace
+from urllib.error import HTTPError
+
+import pytest
+
+from secrets_engine import cli, engine_auth
+from secrets_engine.errors import BackendError
+from secrets_engine.openbao import OpenBaoClient, ScopedTokenSession
+from secrets_engine.service_auth import (
+    KeyCapeServiceAuthProvider,
+    OpenBaoOidcClientSecretSource,
+)
+from tests.test_engine_auth import _cfg, _jwt_contract
+from tests.test_service_auth import _jwt
+
+SECRET = "synthetic-client-secret-0123456789"
+OP_TOKEN = "synthetic-operator-token-abcdef"
+OP_ACCESSOR = "synthetic-operator-accessor"
+AMBIENT = "ambient-token-must-not-be-used"
+ADDR = "https://bao.example.test"
+
+
+class _Resp:
+    def __init__(self, body: bytes, status: int = 200):
+        self.status, self._body = status, body
+
+    def read(self, _n=-1):
+        return self._body
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *_):
+        return False
+
+
+class FakeBao:
+    def __init__(self, kv_status=200, revoke_status=204):
+        self.kv_status, self.revoke_status = kv_status, revoke_status
+        self.argv, self.env, self.requests = [], [], []
+
+    def runner(self, argv, env):
+        self.argv.append(list(argv))
+        self.env.append(dict(env))
+        out = {"auth": {"client_token": OP_TOKEN, "accessor": OP_ACCESSOR}}
+        return 0, json.dumps(out).encode()
+
+    def transport(self, request, *, timeout):
+        self.requests.append(
+            (request.get_method(), request.full_url, dict(request.header_items()))
+        )
+        if request.full_url.endswith("/v1/platform/data/workloads/keycape/secrets-engine-openbao"):
+            if self.kv_status != 200:
+                raise HTTPError(request.full_url, self.kv_status, "denied", {}, None)
+            return _Resp(json.dumps({"data": {"data": {"CLIENT_SECRET": SECRET}}}).encode())
+        if request.full_url.endswith("/v1/auth/token/revoke-self"):
+            return _Resp(b"", self.revoke_status)
+        pytest.fail(f"unexpected request {request.full_url}")
+
+
+def _source(fake, **kw):
+    return OpenBaoOidcClientSecretSource(
+        bao_addr=ADDR, runner=fake.runner, transport=fake.transport, **kw
+    )
+
+
+def _assert_no_leak(fake, *texts):
+    for value in (SECRET, OP_TOKEN, OP_ACCESSOR):
+        for argv in fake.argv:
+            assert value not in " ".join(argv)
+        for env in fake.env:
+            assert value not in " ".join(f"{k}={v}" for k, v in env.items())
+        assert value not in " ".join(f"{k}={v}" for k, v in os.environ.items())
+        for text in texts:
+            assert value not in text
+
+
+def _assert_no_files(root):
+    for dirpath, _dirs, files in os.walk(root):
+        for name in files:
+            data = open(os.path.join(dirpath, name), "rb").read()
+            assert SECRET.encode() not in data and OP_TOKEN.encode() not in data
+
+
+def test_reads_in_memory_with_header_only_and_revokes(monkeypatch, tmp_path, capsys):
+    monkeypatch.setenv("BAO_TOKEN", AMBIENT)
+    monkeypatch.setenv("VAULT_TOKEN", AMBIENT)
+    monkeypatch.setenv("HOME", str(tmp_path))
+    fake = FakeBao()
+    src = _source(fake)
+    assert src() == SECRET
+    assert fake.argv == [[
+        "bao", "login", "-method=oidc", "-path=netkingdom", "-no-store",
+        "-format=json", "role=keycape-secrets-engine-openbao-operator-workload-kv-read",
+    ]]
+    env = fake.env[0]
+    assert "BAO_TOKEN" not in env and "VAULT_TOKEN" not in env
+    assert env["BAO_ADDR"] == ADDR
+    (get, kv_url, kv_headers), (post, rv_url, rv_headers) = fake.requests
+    assert (get, post) == ("GET", "POST")
+    assert kv_url == ADDR + "/v1/platform/data/workloads/keycape/secrets-engine-openbao"
+    assert rv_url == ADDR + "/v1/auth/token/revoke-self"
+    for headers in (kv_headers, rv_headers):
+        assert headers["X-vault-token"] == OP_TOKEN
+        assert AMBIENT not in json.dumps(headers)
+    ev = src.evidence()
+    assert ev == {
+        "secret_source": "openbao-oidc-in-memory",
+        "operator_session_handle": ev["operator_session_handle"],
+        "operator_revocation_attempted": True,
+        "operator_revocation_succeeded": True,
+    }
+    assert len(ev["operator_session_handle"]) == 12
+    out, err = capsys.readouterr()
+    _assert_no_leak(fake, out, err, repr(src), json.dumps(ev))
+    _assert_no_files(tmp_path)
+
+
+def test_revoke_self_runs_when_kv_read_is_denied(capsys):
+    fake = FakeBao(kv_status=403)
+    src = _source(fake)
+    with pytest.raises(BackendError, match="HTTP 403") as error:
+        src()
+    assert [r[0] for r in fake.requests] == ["GET", "POST"]
+    assert src.revocation_attempted and src.revocation_succeeded
+    _assert_no_leak(fake, str(error.value), *capsys.readouterr())
+
+
+def test_failed_login_makes_no_request():
+    fake = FakeBao()
+    src = _source(fake)
+    src.runner = lambda argv, env: (2, b"")
+    with pytest.raises(BackendError, match="exit 2"):
+        src()
+    assert fake.requests == []
+
+
+@pytest.mark.parametrize(
+    "override",
+    [
+        {"oidc_role": "platform-admin"},
+        {"oidc_mount": "oidc"},
+        {"kv_path": "workloads/keycape/other"},
+        {"kv_field": "OTHER"},
+    ],
+)
+def test_coordinates_are_pinned(override):
+    with pytest.raises(BackendError, match="reviewed plan"):
+        _source(FakeBao(), **override)
+
+
+@pytest.mark.parametrize("addr", ["http://bao.example.test", "ftp://x", "", "https://u:p@bao"])
+def test_address_must_be_https_or_loopback(addr):
+    with pytest.raises(BackendError):
+        OpenBaoOidcClientSecretSource(bao_addr=addr)
+    OpenBaoOidcClientSecretSource(bao_addr="http://127.0.0.1:8200")
+
+
+def test_engine_refuses_consumer_file_for_openbao_profile(tmp_path):
+    secret = tmp_path / "client.secret"
+    secret.write_text(SECRET)
+    secret.chmod(0o600)
+    cfg = _cfg(
+        tmp_path,
+        openbao_jwt_login_file=_jwt_contract(tmp_path),
+        keycape_token_url="https://keycape.example.test/token",
+        keycape_issuer="https://keycape.example.test",
+        keycape_client_secret_file=secret,
+    )
+    with pytest.raises(BackendError, match="refused for the secrets-engine-openbao") as error:
+        engine_auth.login_service_jwt(cfg)
+    assert SECRET not in str(error.value)
+
+
+def test_probe_end_to_end_is_value_free(tmp_path, monkeypatch, capsys):
+    monkeypatch.setenv("BAO_TOKEN", AMBIENT)
+    monkeypatch.setenv("HOME", str(tmp_path))
+    fake = FakeBao()
+    keycape_auth = []
+
+    def keycape_transport(request, *, timeout):
+        keycape_auth.append(request.get_header("Authorization"))
+        return _Resp(json.dumps(
+            {"access_token": _jwt(), "token_type": "Bearer", "expires_in": 900}
+        ).encode())
+
+    monkeypatch.setattr(
+        engine_auth, "OpenBaoOidcClientSecretSource",
+        functools.partial(
+            OpenBaoOidcClientSecretSource, runner=fake.runner, transport=fake.transport
+        ),
+    )
+    monkeypatch.setattr(
+        engine_auth, "KeyCapeServiceAuthProvider",
+        functools.partial(KeyCapeServiceAuthProvider, transport=keycape_transport),
+    )
+    monkeypatch.setattr("secrets_engine.service_auth.preflight_service_jwt",
+                        lambda token, config, now=None: SimpleNamespace(token=token))
+    jwt_logins = []
+
+    def fake_login_jwt(self, mount, role, jwt):
+        jwt_logins.append((mount, role))
+        client = OpenBaoClient(addr=self.addr, token="engine-token", bao_bin="bao")
+        monkeypatch.setattr(client, "_run_ok", lambda args, **_k: "")
+        return ScopedTokenSession(client=client, accessor_fingerprint="0123456789ab")
+
+    monkeypatch.setattr(OpenBaoClient, "login_jwt", fake_login_jwt)
+    cfg = _cfg(
+        tmp_path,
+        bao_addr=ADDR,
+        openbao_jwt_login_file=_jwt_contract(tmp_path),
+        keycape_token_url="https://keycape.example.test/token",
+        keycape_issuer="https://keycape.example.test",
+    )
+    monkeypatch.setattr(cli.Config, "load", classmethod(lambda _cls: cfg))
+    rc = cli.main(["service-auth", "probe-openbao", "--json"])
+    out, err = capsys.readouterr()
+    assert rc == 0, err
+    payload = json.loads(out)
+    assert payload["ok"] is True
+    assert payload["secret_source"] == "openbao-oidc-in-memory"
+    assert payload["operator_revocation_succeeded"] is True
+    assert payload["revocation_succeeded"] is True
+    assert len(jwt_logins) == 1
+    assert len(keycape_auth) == 1 and keycape_auth[0].startswith("Basic ")
+    _assert_no_leak(fake, out, err)
+    _assert_no_files(tmp_path)
diff --git a/tests/test_service_auth.py b/tests/test_service_auth.py
index 6c0b271..beb8578 100644
--- a/tests/test_service_auth.py
+++ b/tests/test_service_auth.py
@@ -45,11 +45,10 @@ def _jwt(**overrides):
     return f"{_segment({'alg': 'RS256', 'typ': 'JWT'})}.{_segment(claims)}.signature"
 
 
-def _config(secret_file=Path("/tmp/keycape-client-secret")):
+def _config(_unused=None):
     return KeyCapeServiceAuthConfig(
         token_url="https://keycape.example.test/token",
         issuer="https://keycape.example.test",
-        client_secret_file=secret_file,
     )
 
 
@@ -114,7 +113,9 @@ def test_exchange_uses_basic_auth_and_never_places_secret_in_body(tmp_path):
             }
         )
 
-    provider = KeyCapeServiceAuthProvider(_config(secret_file), transport=transport)
+    provider = KeyCapeServiceAuthProvider(
+        _config(), transport=transport, secret_source=lambda: "client-secret-value"
+    )
     result = provider.exchange(now=NOW)
     assert result.expires_at == int(NOW.timestamp()) + 900
     assert captured["authorization"].startswith("Basic ")
@@ -138,7 +139,9 @@ def test_exchange_rejects_refresh_or_id_tokens_without_exposing_secret(tmp_path)
             }
         )
 
-    provider = KeyCapeServiceAuthProvider(_config(secret_file), transport=transport)
+    provider = KeyCapeServiceAuthProvider(
+        _config(), transport=transport, secret_source=lambda: secret
+    )
     with pytest.raises(BackendError, match="forbidden extra token") as error:
         provider.exchange(now=NOW)
     assert secret not in str(error.value)
@@ -149,12 +152,24 @@ def test_provider_config_is_exact_and_has_no_bootstrap_fallback():
         KeyCapeServiceAuthConfig(
             token_url="http://keycape.example.test/token",
             issuer="https://keycape.example.test",
-            client_secret_file=Path("/tmp/unused"),
         )
     with pytest.raises(BackendError, match="accepted contract"):
         KeyCapeServiceAuthConfig(
             token_url="https://keycape.example.test/token",
             issuer="https://keycape.example.test",
-            client_secret_file=Path("/tmp/unused"),
             client_id="operator",
         )
+
+
+def test_openbao_profile_refuses_file_source(tmp_path):
+    with pytest.raises(BackendError, match="file source is refused"):
+        KeyCapeServiceAuthConfig(
+            token_url="https://keycape.example.test/token",
+            issuer="https://keycape.example.test",
+            client_secret_file=tmp_path / "client.secret",
+        )
+    provider = KeyCapeServiceAuthProvider(
+        _config(), transport=lambda *_a, **_k: pytest.fail("no exchange")
+    )
+    with pytest.raises(BackendError, match="no file fallback"):
+        provider.exchange(now=NOW)
diff --git a/workplans/SECRETS-WP-0012-keycape-openbao-consumer-custody.md b/workplans/SECRETS-WP-0012-keycape-openbao-consumer-custody.md
index 90c9baf..f331d7f 100644
--- a/workplans/SECRETS-WP-0012-keycape-openbao-consumer-custody.md
+++ b/workplans/SECRETS-WP-0012-keycape-openbao-consumer-custody.md
@@ -25,6 +25,12 @@ approved the two-copy custody boundary (decision
 `632a8893-0d6a-4591-a50b-40bbdb798f32`), not generation, fetch, delivery,
 registration or deployment. Live service-JWT adoption stays SECRETS-WP-0008-T06.
 
+Redirected 2026-10-06: founder direction keeps the secret only in OpenBao, and
+the ops-mason plan `keycape-secrets-engine-openbao-client-custody` (658cdbc)
+replaces the consumer file with a per-command in-memory read (T02 cancelled,
+T04 implements it, T03 is the first live use). T01's file checks remain for
+the approval client only.
+
 Packet: [docs/keycape-openbao-consumer-custody.md](../docs/keycape-openbao-consumer-custody.md).
 
 ## Consumer packet and strict file acceptance
@@ -48,28 +54,51 @@ suite: 510 passed, 1 skipped (root-only owner test).
 
 ```task
 id: SECRETS-WP-0012-T02
-status: wait
-needs_human: true
+status: cancel
 priority: high
-blocked_on: founder
-blocking_reason: "Host (workstation), OS user (worsch), persistent storage and rotation cadence are recommendations awaiting founder acceptance; the custody child cannot be finalized without them."
 state_hub_task_id: "b95da704-ce13-5bf5-be3b-126e894a669d"
 ```
 
-## Attended consumer-copy delivery
+Cancelled 2026-10-06: superseded by founder direction 2026-10-06 (the client
+secret lives only in OpenBao, no workstation copy) and the ops-mason plan
+`keycape-secrets-engine-openbao-client-custody` (658cdbc, MASON-WP-0009).
+D1-D4 (host, OS user, persistent file, rotation cadence) no longer apply.
+
+## In-memory OpenBao secret source
+
+```task
+id: SECRETS-WP-0012-T04
+status: done
+priority: high
+```
+
+Done 2026-10-06. `service_auth.OpenBaoOidcClientSecretSource`: attended
+`bao login -method=oidc -path=netkingdom -no-store -format=json` on role
+`keycape-secrets-engine-openbao-operator-workload-kv-read`, token from a
+stdout pipe, ambient `BAO_TOKEN`/`VAULT_TOKEN` stripped, header-only GET of
+`platform/data/workloads/keycape/secrets-engine-openbao` field
+`CLIENT_SECRET`, unconditional `revoke-self`, then the KeyCape exchange and
+OpenBao JWT login. The file source is refused for this profile (kept for the
+approval client). `secrets-engine service-auth probe-openbao` prints
+value-free evidence. Synthetic tests: `tests/test_openbao_secret_source.py`.
+Docs: `docs/keycape-openbao-consumer-custody.md` (rewritten),
+`docs/service-auth.md`, `docs/cli.md`.
+
+## First live attended use
 
 ```task
 id: SECRETS-WP-0012-T03
 status: wait
 needs_human: true
-depends_on: [SECRETS-WP-0012-T02]
 priority: high
-blocked_on: message-from:railiance-platform
-blocking_reason: "Requires the founder-approved CCR-2026-0033 custody child, executed attended on the named host. Platform generates and writes both copies in one process. secrets-engine records only the check-secret-file result. No client-side OpenBao read."
+blocked_on: founder
+blocking_reason: "Founder runs the attended probe-openbao command in docs/keycape-openbao-consumer-custody.md after plan approval A1-A3, the revised CCR-2026-0033 objects applied by railiance-platform, the KeyCape registration live (KEY-WP-0037) and the JWT login contract published."
 state_hub_task_id: "1c3afd34-4aa3-5484-a9c7-2db577225269"
 ```
 
-Acceptance: receipt carries `check-secret-file --json` with `ok: true` and
-no value, length or hash. A failed write leaves no consumer file and is
-recovered by rotation, not by a KV read. First live exchange evidence belongs
-to KEY-WP-0037-T04, and OpenBao login proof belongs to SECRETS-WP-0008-T06.
+Acceptance: the one-line JSON from `service-auth probe-openbao --json` with
+`ok: true`, `secret_source: openbao-oidc-in-memory`, both accessor
+fingerprints and both revoke-self results true, recorded without any value,
+token or full accessor. This is the evidence for KEY-WP-0037-T04,
+RPF-WP-0035-T02 and plan verification item 6; OpenBao login proof also
+closes into SECRETS-WP-0008-T06.