python + typescript + bash: mirror the durability fixes from go/

Parity pass on the other three language templates. Same guarantees as
go/: survive server restart, client restart, half-open TCP, and long
outages; rejoin and drain prime-side backlog on reconnect, without
the user writing any of this in process.*.

python/main.py:
- grpc.keepalive_time_ms=10000, keepalive_timeout_ms=3000,
  keepalive_permit_without_calls=1 on the channel. Half-open TCP is
  detected within ~13s instead of the OS default ~2h.
- Exponential backoff with jitter; max_backoff_seconds config ceiling
  (default 120). Attempts counter resets after a session runs
  healthy for 60s so transient restarts don't escalate the delay.
- chain_id added as a required config field and sent as the
  x-chain-id gRPC metadata header (prime rejects streams without it).

typescript/src/main.ts:
- Same keepalive options on the @grpc/grpc-js client.
- Same exponential backoff + jitter logic.
- chain_id added to Config + metadata.

bash/:
- Config + README updated. The bash template uses Python's main.py
  as its runtime, so the behavioural changes above flow through
  without a separate main per language.

Docs: each README gains a "Durability guarantees" section so contract
authors see the invariants without reading the runtime code.

python/README.md

@@ -36,6 +36,7 @@ A Python-based smart contract client for Dragonchain Prime that connects via gRP
 4. **Configure your connection** by editing `config.yaml`:
    ```yaml
    server_address: "your-dragonchain-server:50051"
+   chain_id: "your-chain-public-id"
    smart_contract_id: "your-smart-contract-id"
    api_key: "your-api-key"
    ```
@@ -52,13 +53,24 @@ A Python-based smart contract client for Dragonchain Prime that connects via gRP
 | Field | Description | Default |
 |-------|-------------|---------|
 | `server_address` | gRPC server address | Required |
+| `chain_id` | Public chain id the SC is registered on (sent as `x-chain-id` metadata) | Required |
 | `smart_contract_id` | Your smart contract ID | Required |
 | `api_key` | API key for authentication | Required |
 | `use_tls` | Enable TLS encryption | `false` |
 | `tls_cert_path` | Path to TLS certificate | - |
 | `num_workers` | Concurrent transaction processors | `10` |
-| `reconnect_delay_seconds` | Delay between reconnection attempts | `5` |
-| `max_reconnect_attempts` | Max reconnect attempts (0 = infinite) | `0` |
+| `reconnect_delay_seconds` | Base delay for exponential backoff between reconnect attempts | `3` |
+| `max_backoff_seconds` | Ceiling for the exponential backoff | `120` |
+| `max_reconnect_attempts` | Max reconnect attempts (0 = infinite, recommended) | `0` |
+
+## Durability guarantees (provided by `main.py`, no work for you)
+
+- **Server restart, update, crash, or network blip** → the client auto-reconnects and resumes processing. Transactions observed while the stream was down stay queued on the Dragonchain Prime side and are delivered (oldest first) on reconnect.
+- **Client restart or long outage** → when this process comes back up (minutes, hours, months later), it rejoins the stream and prime re-delivers every still-pending transaction that should have invoked it.
+- **Half-open TCP** (silent peer, resumed laptop, corporate NAT dropping idle flows) is detected within ~13 seconds via gRPC keepalive and triggers a reconnect. No dangling ghost streams.
+- **Reconnect storms** are avoided: exponential backoff with jitter means many clients reconnecting after a server restart don't all slam `accept()` at the same instant. The timer resets after a stream has been healthy for 60 seconds.
+
+These are invariants of the template — you do not add any of this in `process.py`.
 
 ## Implementing Your Smart Contract