fix(deploy): AI ignoreCommand builds on git errors instead of failing (#119)

CHANGELOG.md

@@ -39,6 +39,8 @@ This file records what changes **in the product** – process and session state
   such leftovers. An approved sample whose export failed is kept (#84).
 
 ### Fixed
+- AI service deployments from `main` no longer end as Error when the last deployed commit is missing from
+  Vercel's shallow clone: the Ignored Build Step now builds on any git error instead of failing (#119).
 - The review page's header fields fit their card at 1280 px: „Quelle anzeigen“ moved under the status, so the
   „Speichern“ button of a correction is no longer scrolled out of sight (#103).
 - Two `pnpm seed:samples` runs for the same company at the same time no longer interfere: the second waits for

docs/technical/deployment-vercel.md

@@ -75,7 +75,9 @@ creation). The script is all-or-nothing; running it twice fails on "role already
    verified 2026-09-27); the first call after that pays a cold start (measured about 5.6 s).
 6. **Builds only when the service changed (#98):** `services/ai/vercel.json` sets an `ignoreCommand` that
    skips the build unless something under `services/ai/` changed since the last successful deployment
-   (`VERCEL_GIT_PREVIOUS_SHA`, else the parent commit; if git cannot compare, it builds). A skipped build
+   (`VERCEL_GIT_PREVIOUS_SHA`, else the parent commit). Vercel skips only on exit 0 and fails the deployment on
+   any code other than 0 or 1, so every git error (e.g. the previous commit is not in the shallow clone) is mapped
+   to exit 1 and the service builds (#119). A skipped build
    ends as `CANCELED`; skipped builds may still count against the plan's deployment limits. A new branch
    without a successful AI deployment compares only its last commit (since #104 only `main` deploys, see
    step 7). **A redeploy runs the same step:** after changing a variable of

services/ai/vercel.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://openapi.vercel.sh/vercel.json",
   "regions": ["fra1"],
-  "ignoreCommand": "git diff --quiet \"${VERCEL_GIT_PREVIOUS_SHA:-HEAD^}\" HEAD -- ./",
+  "ignoreCommand": "git diff --quiet \"${VERCEL_GIT_PREVIOUS_SHA:-HEAD^}\" HEAD -- ./ 2>/dev/null || exit 1",
   "git": {
     "deploymentEnabled": {
       "**": false,