feat(agentic-engineer): take a single-writer lease before a run touches memory

.github/workflows/ci.yaml

@@ -612,6 +612,7 @@ jobs:
               - 'scripts/tests/test-coroot-helper-image-pull-policy.sh'
               - 'scripts/tests/test-agentic-engineer-schedule.sh'
               - 'scripts/tests/test-agentic-engineer-lane-store.sh'
+              - 'scripts/tests/test-agentic-engineer-lane-store-lease.sh'
               - 'scripts/tests/test-kagent-claude-harness-wrapper.sh'
               - 'scripts/kagent-claude-harness/**'
               - 'scripts/tests/test-anthropic-proxy-envoy-config.sh'
@@ -2886,6 +2887,16 @@ jobs:
           shellcheck scripts/tests/test-agentic-engineer-lane-store.sh
           bash scripts/tests/test-agentic-engineer-lane-store.sh
 
+      - name: 🔒 Validate the Agentic Engineer lane store lease
+        if: needs.changes.outputs.k8s == 'true'
+        # Runs the store's pinned rclone image with its own arguments: the lease a
+        # run takes on memory/ refuses every other run, even many at once, the
+        # store refuses a write there without its token, and after a restart the
+        # former holder can neither write nor release.
+        run: |
+          shellcheck scripts/tests/test-agentic-engineer-lane-store-lease.sh
+          bash scripts/tests/test-agentic-engineer-lane-store-lease.sh
+
       - name: 🧠 Validate the kagent harness plugin wrapper
         if: needs.changes.outputs.k8s == 'true'
         # Runs the image's real `claude` wrapper against a stub Claude Code: a

k8s/providers/hetzner/apps/agentic-engineer/deployment-lane-store.yaml

@@ -5,7 +5,14 @@
 #
 # - webdav (8080): read and write, behind the lane-store credential. Only
 #   Substrate's egress gateway reaches it, sending that credential in place of
-#   the agent's placeholder (egress-policy-lane-store.yaml).
+#   the agent's placeholder (egress-policy-lane-store.yaml). It also holds
+#   the lane's single-writer lease, a WebDAV LOCK on memory/ kept only in
+#   its memory, and refuses a write under memory/ without that lock's token
+#   (devantler-tech/monorepo#4910). Lock tokens count up from the second the
+#   store started, so a run trusts one only once it is a minute behind the
+#   store's clock; this relies on node clocks agreeing within a minute. A run
+#   that dies before releasing the lease leaves it held, and every later run
+#   stops at it; restarting this Deployment frees it.
 # - reader (8081): read only, with no credential of its own. Only the
 #   Kubernetes API server reaches it, so a reader needs the
 #   services/proxy grant in role-lane-store-reader.yaml.

k8s/providers/hetzner/apps/agentic-engineer/job-schedule.yaml

@@ -97,26 +97,68 @@ spec:
                 Scheduled run of the devantler-tech Agentic Engineer on its kagent lane:
                 instance `kagent-cluster`, writer namespace `kagent/*`, one run a day.
 
-                1. Restore your native memory from the lane store. List memory/ with a
-                   WebDAV PROPFIND (`curl -fsS -X PROPFIND -H 'Depth: 1'` plus the store
-                   header) and download every file into ~/lane-memory/. Only a 404 for
-                   memory/ means a first run, so start with an empty ~/lane-memory/. Any
-                   other failure means the store is unreachable: stop and report it.
-                2. Shallow-clone devantler-tech/monorepo, read its AGENTS.md, load the
+                1. Take the lane store's single-writer lease: an exclusive WebDAV lock
+                   on memory/ that also fences every write under it, so that overlapping
+                   runs never overwrite each other's memory (devantler-tech/monorepo#4910).
+                   Read every status with `curl -sS -D -`, not -f, which hides it.
+                   a. Send a PROPFIND to memory/ with the store header and `Depth: 0`.
+                      A 404 means a first run: create memory/ with a MKCOL. Any reply
+                      but 207 or that 404 stops the run.
+                   b. Send a LOCK to memory/ with the store header, `Timeout: Infinite`
+                      and `Content-Type: application/xml`, and this body with OWNER
+                      replaced by `agentic-engineer`, your UTC start time and a random
+                      16-hex-digit nonce, which is your owner:
+                      `<?xml version="1.0"?><D:lockinfo xmlns:D="DAV:"><D:lockscope><D:exclusive/></D:lockscope><D:locktype><D:write/></D:locktype><D:owner>OWNER</D:owner></D:lockinfo>`
+                      A 200 means you hold the lease: keep the reply's Lock-Token value,
+                      angle brackets included. A 423 means another run holds it, or a
+                      run that crashed left it behind: stop, upload nothing and report
+                      it. Never remove a lease you did not take. Any other reply also
+                      stops the run before it touches memory.
+                   c. The store numbers its tokens up from the second it started, and an
+                      UNLOCK checks only the token, so a restarted store could hand your
+                      token to another run whose lease your UNLOCK would then release.
+                      Your token is safe once its number is at least 60 below a reply's
+                      Date header in Unix seconds: no restart can reissue it then, since
+                      the cluster keeps its nodes' clocks within a minute of each other.
+                      Until it is safe, never UNLOCK it. If the LOCK reply shows it is not yet
+                      safe, the store started moments ago: wait out the difference plus
+                      a second, if that is under 10 minutes, then refresh the lease as in
+                      step 4 and check again. If it is still not safe, or the refresh
+                      fails or names another owner, upload nothing, leave the lease
+                      alone and report it.
+                2. Restore your native memory from the lane store: list memory/ with a
+                   PROPFIND (`-X PROPFIND -H 'Depth: 1'` plus the store header), list
+                   each folder it shows the same way, and download every file into
+                   ~/lane-memory/, which stays empty on a first run. A listing or
+                   download you cannot complete stops the run: release the lease with
+                   the UNLOCK of step 4, upload nothing and report it.
+                3. Shallow-clone devantler-tech/monorepo, read its AGENTS.md, load the
                    agentic-engineering plugin and invoke its agentic-engineer entrypoint
                    as this scheduled run. ~/lane-memory/ is your native memory (the
                    legacy layout), as the durable-memory guide says for this lane.
                    Follow the consumer contract and fail closed on missing deployment
                    facts. Do not duplicate the role here.
-                3. Before you stop, however the run ended, upload ~/lane-memory/ back to
-                   memory/ on the lane store, and upload this session's transcript (the
-                   newest Claude Code session JSONL under your Claude config directory)
-                   and your run report to runs/<UTC date>/transcript.jsonl and
+                4. Before you stop, however the run ended, refresh the lease: a LOCK to
+                   memory/ with the store header, `Timeout: Infinite`, no body, and your
+                   Lock-Token value in parentheses as the If header (`If: (<t>)` for
+                   `Lock-Token: <t>`). You still hold the lease only if the reply is 200
+                   and its owner is yours. On any other reply, upload nothing, leave the
+                   lease alone and report it. Otherwise upload ~/lane-memory/ back to
+                   memory/ one file at a time, with that same If header on every PUT and
+                   on the MKCOL of any folder inside memory/: the store refuses a write
+                   under memory/ that lacks the lease's token, and a second write with
+                   one token while the first is still running. A 412 or 423 means you
+                   lost the lease: stop uploading, leave the lease alone and report it.
+                   Then upload this session's transcript (the newest
+                   Claude Code session JSONL under your Claude config directory) and your
+                   run report, with no If header, to runs/<UTC date>/transcript.jsonl and
                    runs/<UTC date>/report.md. If an earlier run that day already wrote
                    them, never replace them: write yours beside them as
                    transcript-<UTC time HHMMSS>.jsonl and report-<UTC time HHMMSS>.md.
                    Create a missing folder with MKCOL before writing into it, and check
-                   that every upload succeeded.
+                   that every upload succeeded. Last, when every write under memory/
+                   succeeded, release the lease: an UNLOCK to memory/ with the store
+                   header and your Lock-Token value as the Lock-Token header.
 
                 This run may open, update and review devantler-tech pull requests and
                 issues, per AGENTS.md. It never merges. Only when genuinely blocked on a