feat(airouter): DeepSeek V4 Flash TDD composite + max-effort template

New code-airouter-deepseekv4flash-tdd-repo/v1 composite (deepseek
methodology + the same tdd-protect/tdd-gate/python-dev/tdd-file-lock
layers as the Qwen TDD composite), plus a task-template that sets
reasoning_effort=max via the new extra_body passthrough (agent-runtimes
TT-38). Model/endpoint/model-registry entries already existed; only
the TDD-capable harness and the template were missing.

harnesses/composites/code-airouter-deepseekv4flash-tdd-repo/v1/harness.yaml

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+kind: composite
+name: code-airouter-deepseekv4flash-tdd-repo
+version: 1
+description: "Airouter DeepSeek V4 Flash code agent with TDD enforcement — tests locked read-only, must pass before finish"
+
+# Inherits airouter context's label gate — only the airouter dispatcher
+# advertises this composite (see dispatcher/poller._collect_supported_harnesses).
+requires_labels: [airouter]
+
+layers:
+  - context: deepseek-code-methodology/v1
+  - context: best-practices/v1
+  - context: airouter/v1
+  - context: gitea-ssh/v1
+  - context: agent-repo/v1
+  - context: tdd-protect/v1
+  - context: tdd-gate/v1
+  - capability: python-dev/v1
+  - capability: tdd-file-lock/v1

task-templates/airouter-code-tdd-deepseekv4flash-max.yaml

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+name: airouter-code-tdd-deepseekv4flash-max
+description: "Airouter DeepSeek V4 Flash code agent (reasoning_effort=max) with TDD enforcement — agentic runner, tests read-only, must pass before finish"
+harness: code-airouter-deepseekv4flash-tdd-repo/v1
+model: DeepSeek-V4-Flash
+runtime_cli: agentic
+extra_body:
+  reasoning_effort: max
+requires_tags: [agentic-runner, coding-agent, git-access, project-repo, best-practices, tdd-gate]
+required_params: [repo_url, agent_repo_url]
+labels: [airouter]
+defaults:
+  timeout: 3600
+  max_turns: 100
+pre_actions:
+  - type: clone
+    repo: "{{ repo_url }}"
+    branch: main
+    depth: 1
+blocked_combinations:
+  - field: on_success
+    contains_type: commit_pr
+    message: "Use agent_repo instead of commit_pr — avoids F77 SSH alias URL bug"
+warnings:
+  - "Airouter agents have no web search — all context must be in the repo or prompt"
+  - "Hard cap: 3 concurrent airouter tasks (DISPATCHER_MAX_TASKS=3 on airouter dispatcher)"
+  - "Test files are locked read-only at the OS level — agent cannot modify them"
+  - "Task will be marked failed if the test suite is not green on completion"
+  - "Use narrow, single-file or single-requirement tasks for best results"
+  - "allowed_failing_tests support requires M19 (pre-test hook) to be deployed"
+  - "reasoning_effort=max is forwarded via extra_body (TT-38, agent-runtimes commit pending) — requires airouter/DeepSeek to honor OpenAI-compatible extra_body passthrough; unverified against airouter.ch's specific proxy behavior as of 2026-07-03"
+  - "New model (released 2026-07): no track record in this codebase yet — treat as experimental until a few tasks land cleanly"