feat(daemon): add fixed repo mode for agents

[lucccf]

What does this PR do?

Adds a "fixed repo" mode that lets agents work in pre-existing local directories instead of per-task worktrees. Currently, every task goes through bare clone → worktree checkout, which fails for large monorepos, non-git VCS (Perforce, SVN), non-GitHub repos, and unversioned directories.

When an agent is configured with fixed_repo_enabled, the daemon selects an idle local path, locks it, injects VCS-aware guidance, and lets the agent work in-place — zero clone overhead.

Resolves #3153.

Type of Change

• New feature (non-breaking change that adds functionality)

Changes Made

Database:

• Added migration 108: four new columns on agent table (fixed_repo_enabled, fixed_repo_paths, vcs_type, cleanup_script)
• Added migration 109: init_script column (entry hook, symmetric to cleanup_script)
• Updated CreateAgent / UpdateAgent SQL queries with COALESCE-based partial update

Handler (API):

• Added fixed repo fields (including init_script) to CreateAgentRequest / UpdateAgentRequest / AgentResponse structs
• UpdateAgent uses pointer fields (*bool, *string) for patch semantics — omitted fields are not changed
• Added vcs_type whitelist validation (git, p4, svn, none) returning 400 on invalid values

Daemon (task execution):

• New fixedRepoLockTable with tryLock/unlock and waitAndLock for path-level exclusive access
  • When all paths are locked, waitAndLock blocks in dispatched state until a path frees (channel notification) instead of failing the task
• runTask branches on Agent.FixedRepoEnabled: fixed-repo path skips execenv.Prepare/Reuse, uses selected path directly
• Optional init script runs before the agent starts; failure blocks the task with reason init_script_failed (5-minute timeout)
• Optional cleanup script runs after the agent exits, regardless of outcome (5-minute timeout)
• Both scripts receive MULTICA_WORK_DIR, MULTICA_TASK_ID, MULTICA_AGENT_ID, MULTICA_AGENT_NAME, MULTICA_VCS_TYPE
• Injects MULTICA_WORK_DIR + MULTICA_FIXED_REPO env vars into agent environment
• Registers task in fixedRepoTasks map for /repo/checkout gate

Health endpoint (repo checkout gate):

• /repo/checkout returns 400 for fixed-repo tasks with a clear error message

Agent brief injection:

• New "Fixed Repository" section replaces "Repositories" when enabled
• New writeVCSGuidance function injects VCS-specific rules (git/p4/svn) with safety constraints
• Unknown VCS types get a generic fallback

CLI:

• Added --fixed-repo-enabled, --fixed-repo-path (repeatable), --vcs-type, --cleanup-script, --init-script flags to agent create and agent update
• Shortened "no fields to update" error message to point to --help

UI (agent detail inspector):

• New FixedRepoSection component in inspector between Properties and Details
• Switch toggle to enable/disable fixed repo mode
• When enabled, pencil icon opens config dialog with VCS type dropdown, path list (add/remove), init/cleanup script inputs
• i18n strings for English and Simplified Chinese

Tests:

• fixed_repo_lock_test.go: exclusive locking, concurrent contention, unknown path handling, waitAndLock blocking/unblock/cancel, multi-path selection, multiple waiter competition
• agent_fixed_repo_test.go: request/response JSON round-trip for all fixed repo fields (including init_script)
• runtime_config_test.go: VCS guidance output verification, fixed repo brief section
• Updated TypeScript test fixtures with new Agent type fields

How to Test

cd server && go build ./...
go test ./internal/daemon/ -run FixedRepo
go test ./internal/daemon/execenv/ -run "VCS|FixedRepo"
go test ./internal/handler/ -run "FixedRepo"

Manual (requires daemon + agent runtime):

1. Create a fixed-repo agent:

   multica agent create --name writer-01 --runtime-id <id>      --fixed-repo-enabled --fixed-repo-path /data/repos/project      --vcs-type git --init-script /data/repos/init.sh --cleanup-script /data/repos/cleanup.sh

2. Assign an issue to the agent → daemon selects the path, agent works in /data/repos/project
3. Verify MULTICA_WORK_DIR is set in agent environment
4. Verify agent brief contains "## Fixed Repository" and "## VCS: git" sections
5. Verify multica repo checkout returns 400 during the task
6. After task ends, verify cleanup script runs and path lock is released
7. With two paths configured, run two concurrent tasks → each gets its own path
8. With all paths locked, assign another task → verify it stays in "dispatched" (Starting) and proceeds when a path frees

UI testing:

1. Open agent detail page in web/desktop
2. Find "Fixed Repository" section between Properties and Details
3. Toggle the switch to enable → verify "Edit" button appears
4. Click Edit → verify dialog opens with VCS Type, Paths, Init Script, Cleanup Script fields
5. Add/remove paths, change VCS type, save → verify changes persisted

Checklist

• I have considered and documented any risks above
• Backward compatible: fixed_repo_enabled=false (default) preserves existing behavior
• Migration is additive only (new columns with defaults)
• I will address all reviewer comments before requesting merge

AI Disclosure

AI tool used: Claude Code (Claude Opus 4.7)

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