The Agent ID rename (PR #7114) introduced four deprecated one-liner
wrapper functions that forward calls to the new AgentID-named functions.
These create a maintenance burden and IDE confusion (autocomplete
suggests the old names). All callers have been migrated:

- Remove ValidateAPIKey(): no non-test callers; remove TestValidateAPIKeyAlias
- Remove GetAPIKey() on Config: no callers outside its own definition
- Remove GetGatewayAPIKeyFromEnv(): no callers outside its own definition
- Rename GenerateRandomAPIKey() → GenerateRandomAgentID(): update the
  single production caller in internal/cmd/root.go and rename all tests
  in internal/auth/apikey_test.go

Also update the stale ValidateAPIKey() reference in the authMiddleware
doc comment in internal/server/middleware.go.

Closes #7136

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

)

🤖 *This PR was created by Repo Assist, an automated AI assistant.*

## Summary

PR #7114 renamed the gateway's "API key" surface to "Agent ID" but left
four deprecated one-liner wrapper functions in place as backwards-compat
aliases. These create IDE confusion (autocomplete surfaces the old
names) and an ongoing maintenance burden. This PR removes them.

## Changes

| Location | Change |
|---|---|
| `internal/auth/header.go` | Remove `ValidateAPIKey()` deprecated
alias; rename `GenerateRandomAPIKey()` → `GenerateRandomAgentID()` |
| `internal/auth/header_test.go` | Remove `TestValidateAPIKeyAlias`
(tests a now-deleted function) |
| `internal/auth/apikey_test.go` | Rename all test functions and call
sites to `GenerateRandomAgentID` |
| `internal/cmd/root.go` | Update the single production caller to use
`GenerateRandomAgentID()` |
| `internal/config/config_core.go` | Remove `GetAPIKey()` deprecated
alias (no non-definition callers) |
| `internal/config/config_env.go` | Remove `GetGatewayAPIKeyFromEnv()`
deprecated alias (no non-definition callers) |
| `internal/server/middleware.go` | Update stale `ValidateAPIKey()`
reference in doc comment |

## Verification

Confirmed no remaining references to the removed/renamed symbols via
`grep` across the full source tree.

## Test Status

Build and tests could not be run — `proxy.golang.org` is blocked in this
environment (pre-existing infrastructure limitation). The changes are
syntactically verified by inspection:
- All callers of removed functions have been updated or removed
- No remaining references to deprecated names in production code or
tests
- The rename is a mechanical sed-replace with no logic changes

Closes #7136




> [!WARNING]
> <details>
> <summary>Firewall blocked 2 domains</summary>
>
> The following domains were blocked by the firewall during workflow
execution:
>
> - `proxy.golang.org`
> - `releaseassets.githubusercontent.com`
>> To allow these domains, add them to the `network.allowed` list in
your workflow frontmatter:
>
> ```yaml
> network:
>   allowed:
>     - defaults
>     - "proxy.golang.org"
>     - "releaseassets.githubusercontent.com"
> ```
>
> See [Network
Configuration](https://github.github.com/gh-aw/reference/network/) for
more information.
>
> </details>


> Generated by [Repo
Assist](https://github.com/github/gh-aw-mcpg/actions/runs/27093463357) ·
sonnet46 8M ·
[◷](https://github.com/search?q=repo%3Agithub%2Fgh-aw-mcpg+%22gh-aw-workflow-id%3A+repo-assist%22&type=pullrequests)
>
<details>
<summary>Add this agentic workflows to your repo</summary>

To install this agentic workflow, run

```
gh aw add githubnext/agentics@851905c
```
</details>


<!-- gh-aw-agentic-workflow: Repo Assist, engine: copilot, version:
1.0.52, model: claude-sonnet-4.6, id: 27093463357, workflow_id:
repo-assist, run:
https://github.com/github/gh-aw-mcpg/actions/runs/27093463357 -->

<!-- gh-aw-workflow-id: repo-assist -->