Today's user-visible bug ("PUT /workspaces/<id>/files/config.yaml: 500
… install: cannot create directory '/opt/configs': Permission denied",
fixed in #2769) shipped to production and was caught only when an
operator opened the Canvas Config tab and clicked Save & Restart on
a claude-code workspace. Two compounding root causes:
1. Path-map fall-through: claude-code wasn't in
workspaceFilePathPrefix, so it fell through to the /opt/configs
default — a path the workspace EC2 doesn't have (cloud-init only
creates /configs).
2. Permission: /configs is root-owned, but the SSH-as-ubuntu install
command had no sudo prefix, so the write would have failed with
EACCES even with the right path.
The synth E2E provisions a fresh workspace every cron firing but
never PUTs a file via the Files API. So neither failure mode could
fail the canary.
Add a new step 7c (between terminal-diagnose and A2A) that:
- PUTs a known marker into config.yaml on each provisioned workspace
- GETs it back and asserts the marker is present
- Fails with an actionable message that names the likely class of
regression (path map vs permission) so the next operator doesn't
have to re-discover today's debugging path
The marker includes the run ID so stale state from a prior canary
can't false-pass.
Why round-trip (not just PUT-and-200): a 200 from PUT only proves the
SSH install succeeded somewhere on disk; the GET-back proves the file
landed at the path the runtime actually reads from (i.e., that the
host:/configs → container:/configs bind-mount sees it). Without the
GET, a future bug that writes to a non-bind-mounted host path would
silently no-op from the runtime's POV but pass the gate.
Deferred (separate PR, requires AWS-creds wiring): a parallel gate
that aws ec2 describe-instances on the workspace EC2 and asserts the
attached IamInstanceProfile.Arn — would directly catch the #466 IAM
profile gap class. Punted because it needs aws-actions/configure-aws-
credentials added to continuous-synth-e2e.yml + a read-only IAM role
provisioned on the AWS side. Tracked as task #301.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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