dsh-tier-router — Tiered model routing for DeepSeek Harness

Routes model steps by task difficulty: a strong tier (deepseek-v4-pro by default) handles planning / architecture / review, while a cheap tier (deepseek-v4-flash by default) handles day-to-day implementation. Inspired by Claude Code's /advisor (consult a stronger model for hard decisions) and opusplan (strong model in plan mode, cheap model for execution), implemented on DeepSeek Harness through its official seams, with an escalation gate, failure auto-escalation, and subagent tiering on top.

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How it works

flowchart LR
    subgraph main["Main session (header-driven)"]
      U["User message"] --> IN["agent/inbox/inserted"]
      IN -->|"auto mode"| HW["write session request/header"]
      PM["plan/mode flip"] --> HW
      HW --> API["api-proxy selection layer"]
      API --> STEP["each step's model = header tier"]
    end
    subgraph child["Subagents (agent/request swap)"]
      W["tier_worker dispatch"] -->|"agentOptions injection"| C["subagent"]
      C --> AR["agent/request waterfall"]
      AR -->|"swap provider/model per tier"| STEP2["subagent steps"]
    end
    G["tools/pre-execute guard"] -.->|"cheap tier + high-impact pattern"| DENY["deny + escalation hint"]
    E["agent/error failures"] -.->|"within window"| ESC["temporary strong tier (TTL)"]

sequenceDiagram
    participant U as User
    participant S as Session (main agent)
    participant A as Strong v4-pro
    participant C as Cheap v4-flash
    U->>S: /tier plan (enter plan mode)
    S->>S: write header -> strong
    S->>A: planning / architecture / design
    U->>S: approve plan, leave plan mode
    S->>S: write header -> cheap
    S->>C: routine implementation
    S->>A: tier_advisor (hard decisions) / tier_review (final review)
    Note over S,C: high-impact actions (rm -rf / credential files) are denied by the guard until the strong tier is selected

Features

• Automatic tiered routing (auto mode, opusplan-style): steps run on the strong tier while plan mode is active and on the cheap tier during execution. Main sessions are routed by writing the session request/header (the official seam the api-proxy selection layer reads, as community plugins like dsh-model-router do); subagents are switched per step at the agent/request waterfall.
• Per-session scoping: /tier strong|cheap|auto|off affects only the current session; other sessions in the process keep their own tier (global default auto). Sessions that should not be managed can opt out with a single /tier off.
• On-demand advice (advisor-style): the /advisor <question> command and the tier_advisor tool hand one decision question plus gathered evidence to the strong tier and return advice / evidence / risks / acceptance criteria; implementation stays on the current tier.
• Review phase: the tier_review tool and /tier review <focus> ask the strong tier to review a change set and return an APPROVE / NEEDS-CHANGES / BLOCKED verdict with issues ranked by severity.
• Failure auto-escalation: repeated step errors within a window (default 2 errors / 60s) temporarily escalate the session to the strong tier (default 180s), expiring via TTL; sessions in off mode never escalate.
• Configurable tiers (durable): /tier set <strong|cheap> <provider> <model> [effort] or the tier_configure tool can point either tier at any registered provider/model (defaults: deepseek-official/deepseek-v4-pro(max) and deepseek-official/deepseek-v4-flash(high)). Configuration persists in the tier-router settings namespace and survives restarts (pass sessionOnly: true for a transient change).
• High-impact escalation gate (deterministic guard): while the cheap tier executes, tools/pre-execute denies high-impact tool calls and requires switching to the strong tier first — no reliance on model self-discipline. Guard rules (pure logic in lib/pure.js, unit-tested):
  • every rm -rf spelling: combined flags (-rf), split flags (-r -f), case variants (-R), long flags (--recursive --force), runner prefixes (sudo rm -rf, busybox rm);
  • destructive commands: mkfs, dd if=, sudo, shutdown/reboot/halt, git push --force/-f, git clean -f*, find ... -delete / find ... -exec rm, python -c with shutil.rmtree / os.remove, curl|sh, wget|sh, chmod on .ssh, chown;
  • sensitive paths: .env (whitelist for .env.example/.template), credentials/secrets with common extensions, .ssh/, private keys such as id_rsa (case-insensitive), .pem, .key;
  • prose never false-positives: echo rm -rf, grep sudo do not trigger (command-position anchored).
• Subagent tiering: tier_worker dispatches bounded task packets to a fresh subagent on a chosen tier (agentOptions model injection), with outputSchema (structured results), toolFilter (restrict worker tools), maxDepth (delegation-depth cap), persona (per-child persona) and background (run via the jobs service); /tier subagent <inherit|cheap|strong> sets the global policy for all other subagent steps.
• Escalation rules injected into the system prompt: ambiguity unresolved, architecture / security / data integrity, two failed attempts, high-risk completion — the model is guided to call tier_advisor / tier_review at decision points.

Installation

Plane note. dsh-tier-router contributes agent-plane surfaces — tools, slash commands, a prompt section, and step-routing listeners — so it must be composed in the agent preset your sessions use, not as a host bundle row. Installing the package alone (or shipping a host insert) activates nothing.

# 1. Link the package into your profile (dev: clone this repo and add the path;
#    once published: dsh plugin --profile web add dsh-tier-router)
git clone https://github.com/BruceLanLan/dsh-tier-router.git
cd dsh-tier-router
dsh plugin --profile web add .

# 2. Install the ready-made agent preset (standard + the tier-routing row) into
#    the user preset root (${DSH_HOME:-$HOME/.dsh}/.agent-presets/):
cp -R agent-presets/tiered "${DSH_HOME:-$HOME/.dsh}/.agent-presets/"

# 3. Make it the default for new sessions (add to the profile's cordis.patch.yml):
#      - id: agent-presets
#        name: '@deepseek-ai/dsh-agent-presets'
#        config:
#          default: tiered
#    (or select "tiered" per session in the preset picker instead)

# 4. Restart DSH (kill the process LISTENing on the web port first), then open a
#    NEW session (existing sessions keep the preset they were created with) and
#    verify with /tier status.

Uninstall: remove the tier-routing row from the preset (or delete the preset directory), and dsh plugin --profile web remove dsh-tier-router to drop the package link.

Installation is verified in practice: the package resolves from the profile store, the shipped agent-presets/tiered preset (a standard copy plus the - id: tier-routing / name: dsh-tier-router row) passes agentPresets.standingKeyFor mount validation, module loading is smoke-tested, and npm pack ships a clean tarball (lib + patch + preset + README/LICENSE).

Usage

Slash commands (typed in the composer; they affect only the current session)

/advisor <question>                          # one strong-tier consultation
/tier status                                # routing state, escalation state, diagnostics
/tier strong | cheap                        # force one tier for this session (optionally persist as session default)
/tier auto                                  # restore auto for this session (plan -> strong, execution -> cheap)
/tier off                                   # disable routing for this session, restore its default model (other sessions unaffected)
/tier plan                                  # auto + enter plan mode, apply the strong header immediately
/tier models                                # list registered providers and their models
/tier set <strong|cheap> <provider> <model> [effort]
/tier subagent <inherit|cheap|strong>       # global policy for subagent steps
/tier review <focus>                        # strong-tier review

Sample output (/tier status):

Tiered model routing
  mode: global=auto, this session=auto (per-session via /tier strong|cheap|auto|off; escalate: 2 errors / 60s window -> 180s strong)
  strong: deepseek-official/deepseek-v4-pro (max)
  cheap:  deepseek-official/deepseek-v4-flash (high)
  subagents: inherit
  diag: requestSteps=42 guardChecks=31 guardDenies=3 headerWrites=4 errorsSeen=0 escalations=0
  session default: deepseek-official/deepseek-v4-pro (max)
  providers: deepseek-official, opencode-go, minimax

Model tools (called by the model when needed)

Tool	Purpose
tier_advisor	Strong-tier consultation: one question + evidence -> advice / risks / acceptance criteria
tier_review	Strong-tier review: change set + validation results -> verdict with ranked issues
tier_route	Set this session's tier (strong/cheap/auto/off, optionally persisted)
tier_configure	Reconfigure either tier's provider/model/effort and the subagent policy
tier_worker	Dispatch a bounded task packet to a subagent on a chosen tier; supports outputSchema / toolFilter / maxDepth / persona
tier_status	Read-only diagnostics: global & session tiers, escalation state, listener counters, effective tier

Configuration

Runtime configuration (no restart needed):

/tier set strong deepseek-official deepseek-v4-pro max
/tier set cheap deepseek-official deepseek-v4-flash high

/tier set and tier_configure persist the tier configuration in the tier-router settings namespace (survives restarts; pass sessionOnly: true for a transient change). tier_route strong|cheap scopes to the current session and does NOT persist by default; pass persist: true to also write the session default model (agent-default-model). Failure auto-escalation parameters (threshold / window / TTL) are currently built-in constants; configurable in a later version.

Tests

npm test        # node:test — 20 cases: guard positive/negative matrix, tier decision precedence, per-session overrides
npm run check   # syntax check for lib/index.js and lib/pure.js

Verified in live multi-round sessions (dynamic-plugin form):

Area	Result
Main-session per-step routing (durable log evidence)	✅ request/header events show the pro -> flash switch
Guard matrix (auto/strong/off)	✅ auto denies / strong allows / off allows + restores default / auto-restored denies
Guard hardening (split flags, runner prefixes, prose, .env whitelist, case)	✅ 7/7 live probes
Tools, positive paths	✅ advisor/review hit the strong tier; route modes; configure; worker on both spawn and fork providers
Worker options	✅ outputSchema structured result, toolFilter restriction, maxDepth rejection, invalid filter error
Tools, negative paths	✅ invalid provider rejected, invalid subagent provider error
Subagent tiering	✅ cheap tier on flash, strong tier on pro (child logs + return values)
Failure-escalation event path	✅ agent/error fires, counters increment, off mode correctly skips
Lifecycle	✅ stop removes guard & tools; re-run restores everything and the guard works
Persistence	✅ agent-default-model written
Cross-turn listener survival	✅ diagnostic counters keep incrementing across turns

FAQ

Q: Why was another session's model switched automatically? Early versions were process-global. Since v0.3.0 /tier commands scope to the current session only; other sessions default to auto independently. A session that should not be managed runs /tier off to opt out.

Q: The tier switch did not take effect immediately? Tier switches are written to the session header before the step is built, so they apply from the next step (one-step delay).

Q: How do I use subscription-channel models (OpenCode Go / MiniMax)? Run /tier models to confirm the provider is registered and its models are configured, then /tier set cheap opencode-go deepseek-v4-flash. pi-ai-style providers must declare baseURL / api / models in settings.yaml, otherwise every model id is rejected.

Q: A high-impact action was blocked. What now? The guard's message tells you: switch to the strong tier first (tier_route strong or /tier strong) and re-issue — the block exists precisely to keep the cheap tier from running destructive actions directly.

Q: /tier does not appear after installing the bundle? The package is an agent-plane plugin: it must be a row in the agent preset your session uses (see Installation). A host bundle row alone activates nothing — agent-plane services (tools, commands, systemPrompt) are only reachable from the preset scope, and this package ships no host insert by design. After adding the row, restart dsh web and verify with /tier status. (The dynamic-plugin form is a process-local temporary instance and disappears on restart.)

Known limitations

• Tier switches take effect from the next step (the header is written before the step builds).
• The subagent global policy (/tier subagent) is process-wide; a worker's per-dispatch tier always wins.
• The full live "fail -> self-heal" sequence for failure auto-escalation has been verified at the event path and unit-logic level; trigger it live per the FAQ if desired.

License

MIT