[TENT] Bind transport policies to intent type

[catyans]

Summary

• carry Request::intent_type into transport policy selection
• allow an optional intent_type filter in configured TENT policies
• preserve catch-all behavior for existing policies and explicit policy_name overrides
• reject invalid intent filters fail-closed by skipping the malformed policy
• document intent-to-transport/QP-pool/SL/TC binding semantics

Compatibility

Policies without intent_type match every intent exactly as before. Requests
with INTENT_UNSPEC therefore retain the existing selection behavior unless an
operator explicitly configures an intent_unspec rule.

Test plan

• clang-format 20
• pre-commit static checks and codespell
• clean TENT CUDA-off build on Ubuntu 24.04 / GCC 13
• six new intent-policy cases repeated 100 times
• tent_transport_selector_test and tent_intent_type_test
• full TENT regression suite: 22/22 passed
• ASan + UBSan build/tests: 2/2 passed, leak detection enabled

Server validation used commit 964a590d, fetched directly from GitHub. The
upstream GitHub Actions matrix is still running; this PR remains Draft until
the TENT CUDA-on/off jobs complete.

[catyans]

This replaces #2839 after migrating the source branch to yanshu/intent-policy-binding. The code commit is unchanged (194ea22); prior discussion and review remain available on #2839.

[gemini-code-assist]

Code Review

This pull request introduces business-intent-based policy binding (intent_type) to the transport selector, allowing requests to match specific QoS and transport policies (such as foreground_get or checkpoint). It also adds command-line benchmark support and comprehensive unit tests. The review feedback highlights a critical issue where request merging does not group by intent_type, potentially causing QoS leakage. Additionally, the reviewer suggests making command-line intent parsing case-insensitive to prevent crashes and explicitly handling null JSON values for intent_type to avoid unexpectedly skipping catch-all policies.

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[gemini-code-assist]

While intent_type is successfully propagated to the selection context here, the request merging logic in mergeRequests (and its helper can_merge) in this file does not check or sort by intent_type. Consequently, requests with different business intents (e.g., foreground_get and background_prefetch) can be merged into a single transfer task, causing one of the intents to be discarded and routed under the other's policy. To prevent this QoS/intent leakage, mergeRequests should be updated to group and merge requests by intent_type as well.

[gemini-code-assist]

The lookup in kIntentTypes is case-sensitive. If a user passes --tent_intent_type with mixed or uppercase characters (e.g., Foreground_Get), the lookup will fail and trigger a crash via LOG_ASSERT. Converting the input string to lowercase before performing the lookup makes the command-line interface more robust and user-friendly.

Suggested change

	auto it = kIntentTypes.find(intent_type);
	LOG_ASSERT(it != kIntentTypes.end())
	<< "Invalid --tent_intent_type=" << intent_type;
	return it->second;
	std::string lower_intent = intent_type;
	std::transform(lower_intent.begin(), lower_intent.end(), lower_intent.begin(),
	[](unsigned char c) { return std::tolower(c); });
	auto it = kIntentTypes.find(lower_intent);
	LOG_ASSERT(it != kIntentTypes.end())
	<< "Invalid --tent_intent_type=" << intent_type;
	return it->second;

[gemini-code-assist]

If a user explicitly configures "intent_type": null in the JSON policy, parseIntentType will return std::nullopt and cause the entire policy to be skipped with a warning. Explicitly handling null values as std::nullopt (which represents a catch-all/no-filter intent) is more robust and prevents unexpected policy skipping.

        if (policy_json.contains("intent_type")) {
            const auto& val = policy_json["intent_type"];
            if (val.is_null()) {
                policy.intent_type = std::nullopt;
            } else {
                auto intent = parseIntentType(val);
                if (!intent.has_value()) {
                    LOG(WARNING)
                        << "Skip policy " << policy.name << ": invalid intent_type";
                    continue;
                }
                policy.intent_type = *intent;
            }
        }

[catyans]

Superseded by ; the final source branch is intent-policy-binding, with the same commit 194ea22.