postdeploy hook fails with exit 3 on first deploy (race with function host startup for connector_extension system key)

## Summary

On a fresh `azd up`, the `postdeploy` hook (`infra/scripts/configure-trigger.sh`) frequently fails with exit code 3 because it tries to read the Function App's `connector_extension` system key before the function host has finished starting and registering it.

## Repro

1. Fresh clone, fresh `azd env new`, fresh `azd up` into an empty resource group.
2. Provision + deploy succeed.
3. Postdeploy hook fires immediately and fails:

```
ERROR: step "cmdhook-postdeploy" failed: 'postdeploy' hook failed with exit code: '3',
Path: '/.../infra/scripts/configure-trigger.sh'.
```

The script emits (from lines 49–54):

> `ERROR: connector_extension system key not found on .`
> `The function host must start once with the connector-triggered agent before the key is created.`

## Root cause

Race between two async events:

1. ARM marks the Function App resource `Done` (what `azd` waits on).
2. The function host inside the app cold-starts, loads the connector-triggered binding, and registers the `connector_extension` system key.

The postdeploy hook runs as soon as (1) completes. On a cold first deploy, (2) hasn't happened yet, so `az functionapp keys list --query systemKeys.connector_extension` returns empty and the script exits 3.

Verified: ~45 seconds later the key was present, and `azd hooks run postdeploy` succeeded on the first retry with no other changes.

## Suggested fix

Add a bounded retry loop around the system-key fetch in `configure-trigger.sh` (and the `.ps1` sibling). Something like:

```bash
echo -e "${CYAN}Fetching connector_extension system key for ${functionAppName}...${NC}"
connectorKey=""
for i in 1 2 3 4 5 6 7 8 9 10; do
connectorKey=$(az functionapp keys list -g "$resourceGroup" -n "$functionAppName" \
--query "systemKeys.connector_extension" -o tsv 2>/dev/null || echo "")
[[ -n "$connectorKey" ]] && break
echo -e "${YELLOW} attempt $i/10: key not registered yet, waiting 15s for host start...${NC}"
sleep 15
done

if [[ -z "$connectorKey" ]]; then
echo -e "${RED}ERROR: connector_extension system key not found on ${functionAppName} after ~150s.${NC}" >&2
echo -e "${RED} Wait a minute and re-run: azd hooks run postdeploy${NC}" >&2
exit 3
fi
```

A 10×15s loop (~2.5 min) comfortably covers a Flex Consumption cold start while still failing fast if something is actually broken (e.g., missing binding, deploy didn't ship the connector-triggered function).

Optional belt-and-suspenders: nudge the host before polling — e.g., `az functionapp restart` followed by a short sleep — but the polling alone should be enough.

## Workaround today

```bash
# wait 30–60s after azd up reports done, then:
azd hooks run postdeploy
```

## Environment

- macOS, `azd` 1.25.6
- `azure-functions-core-tools` v4
- Fresh `rg-m365-test1`, default region

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Empieza por infra/scripts/configure-trigger.sh y su equivalente .ps1, centrándote en la obtención de system-key alrededor de las líneas indicadas 49–54. Reprodúcelo con un azd up nuevo y, después, verifica que el polling acotado permite que el hook postdeploy finalice correctamente cuando aparece la clave connector_extension, y que sigue terminando con 3 después de los reintentos si continúa ausente.

Escrito por el modelo de indexación a partir del texto del issue.