Request validation and resilience improvements (#864)

### Security: Input validation & path safety
- **Reject local file references by default** in package parsing — only allow when explicitly opted in by the service (`ParseFlags::kAllowLocalReferences`) and validated by an `ILocalRefPolicy` (fail-closed: no policy = rejected)
- **`DataRootLocalRefPolicy`** restricts local ref paths to the server's data root via canonical path prefix matching
- **Validate attachment hashes** in compute HTTP handlers — decompresses and re-hashes each attachment at ingestion time to reject tampered payloads
- **Path traversal validation** for worker descriptions (`pathvalidation.h`) — rejects absolute paths, `..` components, Windows reserved device names, and invalid filename characters
- **Harden CbPackage parsing** against corrupt inputs — overflow-safe attachment count, bounds checks on local ref offset/size, graceful failure instead of `ZEN_ASSERT` for untrusted data
- **Harden legacy package parser** — reject zero-size binary fields, missing mappers, and optionally validate resolved attachment hashes
- **Bounds check in `CbPackageReader::MarshalLocalChunkReference`** — detect when `MakeFromFile` silently clamps offset+size to file size

### Reliability: Lock consolidation & bug fixes
- **Consolidate three action map locks into one** (`m_ActionMapLock`) — eliminates deadlock risk from multi-lock ordering, simplifies state transitions, and fixes a race where newly enqueued actions were briefly invisible to `GetActionResult`/`FindActionResult`
- **Fix infinite loop in `BaseRunnerGroup::SubmitActions`** when actions exceed total runner capacity — cap round-robin at `TotalCapacity` and default unassigned results to "No capacity"
- **Fix `MakeSafeAbsolutePathInPlace` for UNC paths** — `\server\share` now correctly becomes `\?\UNC\server\share` instead of `\?\server\share`
- **Fix `max_retries=0`** — previously fell through to the default of 3; now correctly means "no retries"

### New: ManagedProcessRunner
- Cross-platform process runner backed by `SubprocessManager` — uses async exit callbacks instead of polling, delegates CPU/memory metrics to the manager's built-in sampler
- `ProcessGroup` (JobObject on Windows, process group on POSIX) for bulk cancellation on shutdown
- `--managed` flag on `zen exec inproc` to select this runner
- Refactored monitor thread lifecycle — `StartMonitorThread()` now called from derived constructors to avoid calling virtual functions from base constructor

### Process management
- **Suppress crash dialogs** via `JOB_OBJECT_UILIMIT_ERRORMODE` + `SEM_NOGPFAULTERRORBOX` in both `WindowsProcessRunner` and `JobObject::Initialize` — prevents WER/Dr. Watson modal dialogs from blocking the monitor thread
- **CREATE_SUSPENDED → AssignProcessToJobObject → ResumeThread** pattern in `WindowsProcessRunner` — ensures job object assignment before process execution
- **Move stdout/stderr callbacks to `Spawn()` parameters** in `SubprocessManager` — prevents race where early output could be missed before callback installation
- Consistent PID logging across all runner types

### Test infrastructure
- **`zentest-appstub`**: Added `Fail` (configurable exit code) and `Crash` (abort / nullptr deref) test functions
- **Compute integration tests**: exit code handling, auto-retry exhaustion, manual reschedule after failure, mixed success/failure queues, crash handling (abort + nullptr), crash auto-retry, immediate query visibility after enqueue
- **Package format tests**: truncated header, bad magic, attachment count overflow, truncated data, local ref rejection/acceptance, policy enforcement (inside/outside root, traversal, no-policy fail-closed)
- **Legacy package parser tests**: empty input, zero-size binary, hash resolution with/without mapper, hash mismatch detection
- **UNC path tests** for `MakeSafeAbsolutePath`

### Misc
- ANSI color helper macros (`ZEN_RED`, `ZEN_BRIGHT_WHITE`, etc.) and `ZEN_BOLD`/`ZEN_DIM`/etc.
- Generic `fmt::formatter` for types with free `ToString` functions
- Compute dashboard: truncated hash display with monospace font and hover for full value
- Renamed `usonpackage_forcelink` → `cbpackage_forcelink`
- Compute enabled by default in xmake config (releases still explicitly disable)

1 files changed, 7 insertions, 5 deletions

diff --git a/src/zencompute/runners/functionrunner.cpp b/src/zencompute/runners/functionrunner.cpp
index 4f116e7d8..67e12b84e 100644
--- a/src/zencompute/runners/functionrunner.cpp
+++ b/src/zencompute/runners/functionrunner.cpp
@@ -164,8 +164,9 @@ BaseRunnerGroup::SubmitActions(const std::vector<Ref<RunnerAction>>& Actions)
 		}
 	}
 
-	// Assign any remaining actions to runners with capacity (round-robin)
-	for (int i = 0; ActionIdx < Actions.size(); i = (i + 1) % RunnerCount)
+	// Assign any remaining actions to runners with capacity (round-robin).
+	// Cap at TotalCapacity to avoid spinning when there are more actions than runners can accept.
+	for (int i = 0; ActionIdx < Actions.size() && ActionIdx < TotalCapacity; i = (i + 1) % RunnerCount)
 	{
 		if (Capacities[i] > PerRunnerActions[i].size())
 		{
@@ -186,11 +187,12 @@ BaseRunnerGroup::SubmitActions(const std::vector<Ref<RunnerAction>>& Actions)
 		}
 	}
 
-	// Reassemble results in original action order
-	std::vector<SubmitResult> Results(Actions.size());
+	// Reassemble results in original action order.
+	// Actions beyond ActionIdx were not assigned to any runner (insufficient capacity).
+	std::vector<SubmitResult> Results(Actions.size(), SubmitResult{.IsAccepted = false, .Reason = "No capacity"});
 	std::vector<size_t>		  PerRunnerIdx(RunnerCount, 0);
 
-	for (size_t i = 0; i < Actions.size(); ++i)
+	for (size_t i = 0; i < ActionIdx; ++i)
 	{
 		size_t RunnerIdx = ActionRunnerIndex[i];
 		size_t Idx		 = PerRunnerIdx[RunnerIdx]++;