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App Insights connection string survives redeploys (durable store)

Motivation

Operators reported that the Application Insights connection string applied in Settings → Telemetry "keeps disappearing." Root cause: the applied connection string only existed as the APPLICATIONINSIGHTS_CONNECTION_STRING env var on the Container App revision. A full azd provision / quick-deploy.sh all re-applies the Bicep template with applicationInsightsConnectionString sourced from the azd env value (empty by default), which wipes the env var. Unlike the Service Bus integration config (persisted in the servicebuspref Table), telemetry had no durable store, so the override was lost on the next full deploy.

User-facing change

  • Applying a connection string ("Apply to server sidecars") now also persists it to a durable single-row Azure Table (appinsightspref).
  • After a full redeploy wipes the env var, the connection string self-heals:
  • the Settings → Telemetry status endpoint reports the persisted value again;
  • backend OpenTelemetry export re-initialises from the persisted value on the next sidecar restart — no extra revision swap, because the fallback is a read, not a re-apply.
  • "Clear server override" now also removes the persisted row, so a cleared override does not resurface.
  • Browser-side behaviour is unchanged; the SPA response shape is identical.

API / IaC diff summary

Backend only (no API contract change, no IaC change):

  • New api/services/app_insights_pref.py — durable store (Table in Container Apps, JSON file locally), mirroring service_bus_pref. get_* never raises.
  • api/services/app_insights_provisioning.py deployment_connection_string() — env var first, else fall back to the persisted row.
  • api/app/telemetry.py — init_telemetry resolves via a new _resolve_connection_string() (env, then persisted fallback) so backend OTel self-heals.
  • api/tasks/azure/app_insights.py — apply persists the value; clear removes it (both best-effort, never masking the deployment result).

Validation evidence

  • uv run pytest -q api/tests/test_app_insights_pref.py api/tests/test_settings_app_insights.py — 18 passed.
  • uv run pytest -q api/tests/test_telemetry_init.py api/tests/test_upgrade_aca_template.py api/tests/test_service_bus_telemetry.py — 27 passed.
  • uv run pytest -q api/tests — 4823 passed, 4 skipped.
  • uv run ruff check on all touched files — clean.