feat(backend): inject MCP servers in CLI passthrough mode per agent

apps/backend/internal/agent/agents/agent.go

@@ -9,6 +9,7 @@ import (
 	"errors"
 	"time"
 
+	"github.com/kandev/kandev/internal/agent/mcpconfig"
 	"github.com/kandev/kandev/internal/agent/usage"
 	"github.com/kandev/kandev/internal/agentruntime"
 	"github.com/kandev/kandev/pkg/agent"
@@ -157,7 +158,10 @@ type PassthroughOptions struct {
 	Resume           bool            // generic "continue last session" (e.g. -c, --resume latest)
 	PermissionValues map[string]bool // e.g. {"auto_approve": true}
 	WorkDir          string
-	MCPConfigPath    string // path to generated MCP config file for passthrough CLIs that support it
+	// MCPArgs are extra argv tokens produced by the agent's MCP passthrough
+	// strategy (e.g. claude's "--mcp-config <path>", codex's repeated "-c
+	// mcp_servers.…" overrides). Appended to the built command.
+	MCPArgs []string
 	// CLIFlagTokens are user-configured CLI flag argv tokens derived from
 	// AgentProfile.CLIFlags (only Enabled entries, shell-tokenised). Appended
 	// verbatim to the built passthrough command, mirroring CommandOptions.
@@ -253,8 +257,11 @@ type PassthroughConfig struct {
 	StabilityWindow   time.Duration
 	ResumeFlag        Param // generic "continue last session" (e.g. NewParam("-c"), NewParam("--resume", "latest"))
 	SessionResumeFlag Param // resume a specific session by ID (e.g. NewParam("--resume"))
-	MCPConfigFlag     Param // flag used to load an MCP config file, e.g. NewParam("--mcp-config", "{mcp_config}")
-	WaitForTerminal   bool
+	// MCPStrategy materializes resolved MCP servers into this CLI's passthrough
+	// shape (config file + flag, repeated -c overrides, project file, or env var)
+	// without touching the user's global config. Nil means no MCP injection.
+	MCPStrategy     mcpconfig.PassthroughMCPStrategy
+	WaitForTerminal bool
 	// AutoInjectPrompt enables writing the task description to the PTY stdin
 	// after the first idle window. Default false preserves today's behavior.
 	AutoInjectPrompt bool

apps/backend/internal/agent/agents/claude_acp.go

@@ -5,6 +5,7 @@ import (
 	_ "embed"
 	"time"
 
+	"github.com/kandev/kandev/internal/agent/mcpconfig"
 	"github.com/kandev/kandev/internal/agent/usage"
 	"github.com/kandev/kandev/pkg/agent"
 )
@@ -44,7 +45,7 @@ func NewClaudeACP() *ClaudeACP {
 				BufferMaxBytes:        DefaultBufferMaxBytes,
 				ResumeFlag:            NewParam("-c"),
 				SessionResumeFlag:     NewParam("--resume"),
-				MCPConfigFlag:         NewParam("--mcp-config", "{mcp_config}"),
+				MCPStrategy:           mcpconfig.ClaudeStrategy{},
 				AutoInjectPrompt:      true,
 				SubmitSequence:        "\r",
 				DisableBracketedPaste: true,

apps/backend/internal/agent/agents/codex_acp.go

@@ -5,6 +5,7 @@ import (
 	_ "embed"
 	"time"
 
+	"github.com/kandev/kandev/internal/agent/mcpconfig"
 	"github.com/kandev/kandev/internal/agent/usage"
 	"github.com/kandev/kandev/pkg/agent"
 )
@@ -56,6 +57,7 @@ func NewCodexACP() *CodexACP {
 				ModelFlag:        NewParam("--model", "{model}"),
 				IdleTimeout:      3 * time.Second,
 				BufferMaxBytes:   DefaultBufferMaxBytes,
+				MCPStrategy:      mcpconfig.CodexStrategy{},
 				AutoInjectPrompt: true,
 				SubmitSequence:   "\r",
 			},

apps/backend/internal/agent/agents/cursor_acp.go

@@ -6,6 +6,7 @@ import (
 	_ "embed"
 	"time"
 
+	"github.com/kandev/kandev/internal/agent/mcpconfig"
 	"github.com/kandev/kandev/internal/agent/usage"
 	"github.com/kandev/kandev/pkg/agent"
 )
@@ -43,6 +44,9 @@ func NewCursorACP() *CursorACP {
 				ModelFlag:      NewParam("--model", "{model}"),
 				IdleTimeout:    3 * time.Second,
 				BufferMaxBytes: DefaultBufferMaxBytes,
+				// cursor-agent has no MCP flag/env; write a project-local
+				// .cursor/mcp.json into the worktree (only if absent).
+				MCPStrategy: mcpconfig.CursorStrategy{},
 			},
 		},
 	}

apps/backend/internal/agent/agents/helpers.go

@@ -104,25 +104,6 @@ func (b *CmdBuilder) Prompt(flag Param, prompt string) *CmdBuilder {
 	return b
 }
 
-// MCPConfig appends an MCP config flag when a passthrough CLI supports one.
-// flag args support {mcp_config} placeholder, e.g. NewParam("--mcp-config", "{mcp_config}").
-func (b *CmdBuilder) MCPConfig(flag Param, path string) *CmdBuilder {
-	if flag.IsEmpty() || path == "" {
-		return b
-	}
-	hasPlaceholder := false
-	for _, arg := range flag.args {
-		if strings.Contains(arg, "{mcp_config}") {
-			hasPlaceholder = true
-		}
-		b.args = append(b.args, strings.ReplaceAll(arg, "{mcp_config}", path))
-	}
-	if !hasPlaceholder {
-		b.args = append(b.args, path)
-	}
-	return b
-}
-
 // Flag appends arbitrary flag parts to the command.
 func (b *CmdBuilder) Flag(parts ...string) *CmdBuilder {
 	b.args = append(b.args, parts...)

apps/backend/internal/agent/agents/opencode_acp.go

@@ -5,6 +5,7 @@ import (
 	_ "embed"
 	"time"
 
+	"github.com/kandev/kandev/internal/agent/mcpconfig"
 	"github.com/kandev/kandev/internal/agent/usage"
 	"github.com/kandev/kandev/pkg/agent"
 )
@@ -43,6 +44,10 @@ func NewOpenCodeACP() *OpenCodeACP {
 				IdleTimeout:    3 * time.Second,
 				BufferMaxBytes: DefaultBufferMaxBytes,
 				ResumeFlag:     NewParam("-c"),
+				// opencode has no MCP flag; write a temp opencode.json and point
+				// it there via the OPENCODE_CONFIG env var (merges, never writes
+				// ~/.config/opencode).
+				MCPStrategy: mcpconfig.OpenCodeStrategy{},
 			},
 		},
 	}

apps/backend/internal/agent/agents/passthrough.go

@@ -27,7 +27,11 @@ func (p *StandardPassthrough) BuildPassthroughCommand(opts PassthroughOptions) C
 	case opts.Prompt != "":
 		b.Prompt(p.Cfg.PromptFlag, opts.Prompt)
 	}
-	b.MCPConfig(p.Cfg.MCPConfigFlag, opts.MCPConfigPath)
+
+	// MCP injection args go last so Claude Code's variadic --mcp-config does not
+	// swallow a positional prompt as an extra config path. Codex's `-c` overrides
+	// are order-insensitive, so trailing placement is safe for them too.
+	b.Flag(opts.MCPArgs...)
 
 	return b.Build()
 }