docs: update deploy-to-testnet.md to note deprecation of para_id in chain specs (#775)

Author: nhussein11

llms.txt

@@ -32621,6 +32621,15 @@ To define your chain specification:
 
     You should now see your chain specification containing SCALE-encoded hex values versus plain text.
 
+
+!!!note "Deprecation of `para_id` in Chain Specs"
+
+    The `para_id` field in JSON chain specifications, added through the [`chain-spec-builder`](https://paritytech.github.io/polkadot-sdk/master/staging_chain_spec_builder/index.html){target=\_blank} command, is currently used by nodes for configuration purposes. However, beginning with Polkadot SDK release `stable2509`, the `para_id` field will no longer be required in chain specifications. Instead, runtimes need to be updated to implement the [`cumulus_primitives_core::GetParachainInfo`](https://paritytech.github.io/polkadot-sdk/master/cumulus_primitives_core/trait.GetParachainInfo.html){target=\_blank} trait to successfully operate with nodes using chain specs that omit the `para_id` field.
+
+    With the upcoming `stable2512` release, the `para_id` field will be completely removed from chain specifications in favor of the new runtime API. New nodes will be unable to start with chain specs containing the `para_id` field unless the runtime implements the `GetParachainInfo` trait. Ensure your runtime is updated to maintain compatibility with future node versions.
+
+    For guidance on performing runtime upgrades to implement this new trait, refer to the [runtime upgrade tutorial](/tutorials/polkadot-sdk/parachains/zero-to-hero/runtime-upgrade/){target=\_blank}.
+
 ## Export Required Files
 
 To prepare the parachain collator to be registered on Paseo, follow these steps:

tutorials/polkadot-sdk/parachains/zero-to-hero/deploy-to-testnet.md

@@ -148,6 +148,15 @@ To define your chain specification:
 
     You should now see your chain specification containing SCALE-encoded hex values versus plain text.
 
+
+!!!note "Deprecation of `para_id` in Chain Specs"
+
+    The `para_id` field in JSON chain specifications, added through the [`chain-spec-builder`](https://paritytech.github.io/polkadot-sdk/master/staging_chain_spec_builder/index.html){target=\_blank} command, is currently used by nodes for configuration purposes. However, beginning with Polkadot SDK release `stable2509`, the `para_id` field will no longer be required in chain specifications. Instead, runtimes need to be updated to implement the [`cumulus_primitives_core::GetParachainInfo`](https://paritytech.github.io/polkadot-sdk/master/cumulus_primitives_core/trait.GetParachainInfo.html){target=\_blank} trait to successfully operate with nodes using chain specs that omit the `para_id` field.
+
+    With the upcoming `stable2512` release, the `para_id` field will be completely removed from chain specifications in favor of the new runtime API. New nodes will be unable to start with chain specs containing the `para_id` field unless the runtime implements the `GetParachainInfo` trait. Ensure your runtime is updated to maintain compatibility with future node versions.
+
+    For guidance on performing runtime upgrades to implement this new trait, refer to the [runtime upgrade tutorial](/tutorials/polkadot-sdk/parachains/zero-to-hero/runtime-upgrade/){target=\_blank}.
+
 ## Export Required Files
 
 To prepare the parachain collator to be registered on Paseo, follow these steps: