feat: implement model-specific Codex instructions for GPT-5

- Added `CodexInstructions(modelName string)` function to dynamically select instructions based on the model (e.g., GPT-5 Codex).
- Introduced `gpt_5_instructions.txt` and `gpt_5_codex_instructions.txt` for respective model configurations.
- Updated translators to pass `modelName` and use the new instruction logic.

internal/misc/codex_instructions.go

@@ -9,5 +9,15 @@ import _ "embed"
 // which is embedded into the application binary at compile time. This variable
 // contains instructional text used for Codex-related operations and model guidance.
 //
-//go:embed codex_instructions.txt
-var CodexInstructions string
+//go:embed gpt_5_instructions.txt
+var GPT5Instructions string
+
+//go:embed gpt_5_codex_instructions.txt
+var GPT5CodexInstructions string
+
+func CodexInstructions(modelName string) string {
+	if modelName == "gpt-5-codex" {
+		return GPT5CodexInstructions
+	}
+	return GPT5Instructions
+}

internal/misc/gpt_5_codex_instructions.txt

@@ -0,0 +1 @@
+"You are Codex, based on GPT-5. You are running as a coding agent in the Codex CLI on a user's computer.\n\n## General\n\n- The arguments to `shell` will be passed to execvp(). Most terminal commands should be prefixed with [\"bash\", \"-lc\"].\n- Always set the `workdir` param when using the shell function. Do not use `cd` unless absolutely necessary.\n- When searching for text or files, prefer using `rg` or `rg --files` respectively because `rg` is much faster than alternatives like `grep`. (If the `rg` command is not found, then use alternatives.)\n\n## Editing constraints\n\n- Default to ASCII when editing or creating files. Only introduce non-ASCII or other Unicode characters when there is a clear justification and the file already uses them.\n- Add succinct code comments that explain what is going on if code is not self-explanatory. You should not add comments like \"Assigns the value to the variable\", but a brief comment might be useful ahead of a complex code block that the user would otherwise have to spend time parsing out. Usage of these comments should be rare.\n- You may be in a dirty git worktree.\n    * NEVER revert existing changes you did not make unless explicitly requested, since these changes were made by the user.\n    * If asked to make a commit or code edits and there are unrelated changes to your work or changes that you didn't make in those files, don't revert those changes.\n    * If the changes are in files you've touched recently, you should read carefully and understand how you can work with the changes rather than reverting them.\n    * If the changes are in unrelated files, just ignore them and don't revert them.\n- While you are working, you might notice unexpected changes that you didn't make. If this happens, STOP IMMEDIATELY and ask the user how they would like to proceed.\n\n## Plan tool\n\nWhen using the planning tool:\n- Skip using the planning tool for straightforward tasks (roughly the easiest 25%).\n- Do not make single-step plans.\n- When you made a plan, update it after having performed one of the sub-tasks that you shared on the plan.\n\n## Codex CLI harness, sandboxing, and approvals\n\nThe Codex CLI harness supports several different configurations for sandboxing and escalation approvals that the user can choose from.\n\nFilesystem sandboxing defines which files can be read or written. The options for `sandbox_mode` are:\n- **read-only**: The sandbox only permits reading files.\n- **workspace-write**: The sandbox permits reading files, and editing files in `cwd` and `writable_roots`. Editing files in other directories requires approval.\n- **danger-full-access**: No filesystem sandboxing - all commands are permitted.\n\nNetwork sandboxing defines whether network can be accessed without approval. Options for `network_access` are:\n- **restricted**: Requires approval\n- **enabled**: No approval needed\n\nApprovals are your mechanism to get user consent to run shell commands without the sandbox. Possible configuration options for `approval_policy` are\n- **untrusted**: The harness will escalate most commands for user approval, apart from a limited allowlist of safe \"read\" commands.\n- **on-failure**: The harness will allow all commands to run in the sandbox (if enabled), and failures will be escalated to the user for approval to run again without the sandbox.\n- **on-request**: Commands will be run in the sandbox by default, and you can specify in your tool call if you want to escalate a command to run without sandboxing. (Note that this mode is not always available. If it is, you'll see parameters for it in the `shell` command description.)\n- **never**: This is a non-interactive mode where you may NEVER ask the user for approval to run commands. Instead, you must always persist and work around constraints to solve the task for the user. You MUST do your utmost best to finish the task and validate your work before yielding. If this mode is paired with `danger-full-access`, take advantage of it to deliver the best outcome for the user. Further, in this mode, your default testing philosophy is overridden: Even if you don't see local patterns for testing, you may add tests and scripts to validate your work. Just remove them before yielding.\n\nWhen you are running with `approval_policy == on-request`, and sandboxing enabled, here are scenarios where you'll need to request approval:\n- You need to run a command that writes to a directory that requires it (e.g. running tests that write to /var)\n- You need to run a GUI app (e.g., open/xdg-open/osascript) to open browsers or files.\n- You are running sandboxed and need to run a command that requires network access (e.g. installing packages)\n- If you run a command that is important to solving the user's query, but it fails because of sandboxing, rerun the command with approval. ALWAYS proceed to use the `with_escalated_permissions` and `justification` parameters - do not message the user before requesting approval fLine truncated

internal/translator/codex/claude/codex_claude_request.go

@@ -39,7 +39,7 @@ func ConvertClaudeRequestToCodex(modelName string, inputRawJSON []byte, _ bool)
 
 	template := `{"model":"","instructions":"","input":[]}`
 
-	instructions := misc.CodexInstructions
+	instructions := misc.CodexInstructions(modelName)
 	template, _ = sjson.SetRaw(template, "instructions", instructions)
 
 	rootResult := gjson.ParseBytes(rawJSON)

internal/translator/codex/gemini/codex_gemini_request.go

@@ -42,7 +42,7 @@ func ConvertGeminiRequestToCodex(modelName string, inputRawJSON []byte, _ bool)
 	out := `{"model":"","instructions":"","input":[]}`
 
 	// Inject standard Codex instructions
-	instructions := misc.CodexInstructions
+	instructions := misc.CodexInstructions(modelName)
 	out, _ = sjson.SetRaw(out, "instructions", instructions)
 
 	root := gjson.ParseBytes(rawJSON)

internal/translator/codex/openai/chat-completions/codex_openai_request.go

@@ -97,7 +97,7 @@ func ConvertOpenAIRequestToCodex(modelName string, inputRawJSON []byte, stream b
 
 	// Extract system instructions from first system message (string or text object)
 	messages := gjson.GetBytes(rawJSON, "messages")
-	instructions := misc.CodexInstructions
+	instructions := misc.CodexInstructions(modelName)
 	out, _ = sjson.SetRaw(out, "instructions", instructions)
 	// if messages.IsArray() {
 	// 	arr := messages.Array()

internal/translator/codex/openai/responses/codex_openai-responses_request.go

@@ -8,7 +8,7 @@ import (
 	"github.com/tidwall/sjson"
 )
 
-func ConvertOpenAIResponsesRequestToCodex(_ string, inputRawJSON []byte, _ bool) []byte {
+func ConvertOpenAIResponsesRequestToCodex(modelName string, inputRawJSON []byte, _ bool) []byte {
 	rawJSON := bytes.Clone(inputRawJSON)
 
 	rawJSON, _ = sjson.SetBytes(rawJSON, "stream", true)
@@ -16,7 +16,7 @@ func ConvertOpenAIResponsesRequestToCodex(_ string, inputRawJSON []byte, _ bool)
 	rawJSON, _ = sjson.SetBytes(rawJSON, "parallel_tool_calls", true)
 	rawJSON, _ = sjson.SetBytes(rawJSON, "include", []string{"reasoning.encrypted_content"})
 
-	instructions := misc.CodexInstructions
+	instructions := misc.CodexInstructions(modelName)
 
 	originalInstructions := ""
 	originalInstructionsResult := gjson.GetBytes(rawJSON, "instructions")

internal/translator/codex/openai/responses/codex_openai-responses_response.go

@@ -19,7 +19,7 @@ func ConvertCodexResponseToOpenAIResponses(ctx context.Context, modelName string
 		if typeResult := gjson.GetBytes(rawJSON, "type"); typeResult.Exists() {
 			typeStr := typeResult.String()
 			if typeStr == "response.created" || typeStr == "response.in_progress" || typeStr == "response.completed" {
-				instructions := misc.CodexInstructions
+				instructions := misc.CodexInstructions(modelName)
 				instructionsResult := gjson.GetBytes(rawJSON, "response.instructions")
 				if instructionsResult.Raw == instructions {
 					rawJSON, _ = sjson.SetBytes(rawJSON, "response.instructions", gjson.GetBytes(originalRequestRawJSON, "instructions").String())
@@ -33,7 +33,7 @@ func ConvertCodexResponseToOpenAIResponses(ctx context.Context, modelName string
 
 // ConvertCodexResponseToOpenAIResponsesNonStream builds a single Responses JSON
 // from a non-streaming OpenAI Chat Completions response.
-func ConvertCodexResponseToOpenAIResponsesNonStream(_ context.Context, _ string, originalRequestRawJSON, requestRawJSON, rawJSON []byte, _ *any) string {
+func ConvertCodexResponseToOpenAIResponsesNonStream(_ context.Context, modelName string, originalRequestRawJSON, requestRawJSON, rawJSON []byte, _ *any) string {
 	scanner := bufio.NewScanner(bytes.NewReader(rawJSON))
 	buffer := make([]byte, 10240*1024)
 	scanner.Buffer(buffer, 10240*1024)
@@ -54,7 +54,7 @@ func ConvertCodexResponseToOpenAIResponsesNonStream(_ context.Context, _ string,
 		responseResult := rootResult.Get("response")
 		template := responseResult.Raw
 
-		instructions := misc.CodexInstructions
+		instructions := misc.CodexInstructions(modelName)
 		instructionsResult := gjson.Get(template, "instructions")
 		if instructionsResult.Raw == instructions {
 			template, _ = sjson.Set(template, "instructions", gjson.GetBytes(originalRequestRawJSON, "instructions").String())