context-router git:20261006.fa6eac5A

Immutable. This exact content never changes and is served at /api/v1/blob/44de13e1e0c3774f.

---
name: context-router
description: 'Resolve the minimum set of knowledge-graph nodes needed for a task before reading any source file. Use at the start of every non-trivial task once a project has a knowledge graph — when changing a subsystem, tracing a bug, planning work, answering a question about how something works, or onboarding. This is the mechanism that keeps a large or multi-repo codebase inside a context window: it decides what to load, what to deliberately skip, and forces the agent to declare both before working. Pairs with the knowledge-graph skill, which builds and lints the graph this one traverses.'
id: skill.context-router
tier: 2
kind: skill
origin: seed
title: context-router — the knowledge rule and the traversal that resolves the minimal node set for a task
owns:
  - rule.knowledge
  - context-router.method
  - context-router.declaration
  - context-router.residency
  - context-router.menu
  - context-router.graph-over-harness
requires:
  - skill.knowledge-graph
peers:
  - skill.validate-knowledge
load_when:
  - "what should I load for this task"
  - "resolve the minimal node set before working"
  - "route a task through the knowledge graph"
  - "declare loaded and skipped nodes"
  - "orient in a large codebase without bulk-reading"
  - "context budget for a change"
  - "which leaves or children of a node to open"
  - "harness default working style conflicts with graph doctrine"
artifacts:
  - templates/prompts/graph-session-bootstrap.md
  - templates/knowledge-graph/_schema.md
  - templates/knowledge-graph/index.md
prevents: A session that opens source files before deciding which few facts the task needs, and never declares what it skipped, so nobody downstream can tell an informed omission from an unread node.
est_tokens: 4048
---

# context-router

A large codebase does not fit in a context window, and loading all of it
makes an agent worse: a model that has read everything has no signal
about what matters. This skill replaces "read around until it feels
familiar" with a traversal that terminates and that you can defend.

This skill owns the knowledge rule (the graph is the source of truth for
*structure and capability*, loaded minimally) and the traversal
algorithm that makes the rule executable.

## The knowledge rule

The project keeps **one LLM-maintained knowledge system** at
`docs/graph/`: the router (`graph-lint.py`) routes over it with
`index.md` as the Tier 1 fallback map, Tier 2 nodes own concise facts, Tier 3
leaf collections hold source-backed depth (libraries, provenance,
product, architecture, APIs, data, prompts, evaluations, plans,
runbooks, specs, decisions, tools). It is the project's only
documentation system; every maintained document is a layer of it.

- **Load minimally, and declare it.** Resolve the minimal node set from
  the router (entry nodes, their `requires:` closure, and only the
  composed depth the task names specifically) and declare what you
  loaded and deliberately skipped. Never bulk-read to get oriented; the
  graph is the orientation. The boundary you chose not to cross is part
  of the work's record: a reader who cannot see it cannot tell an unread
  node from a read one. The algorithm below is the full form of this
  obligation; the delegation-boundary form is
  `docs/graph/templates/prompts/graph-session-bootstrap.md`.
- **One home per fact.** Every fact lives in exactly one node's `owns:`;
  everything else links. Duplicated facts rot asymmetrically.
  `graph-lint.py` enforces unique fact-keys, resolvable acyclic edges,
  and no version pin outside its owning library page. The code-side twin
  is **one owner per concern**: a cross-cutting behaviour (session and
  auth, policy emission, tolerant parsing, resource creation, a
  datastore) has exactly one owning component, and a new need extends
  that owner, because two mechanisms multiply precedence questions
  nobody can answer.
- **Graph before code, ahead of memory.** Memory of APIs and versions is
  unreliable; the graph is local and source-grounded. No wiki page for a
  library you're about to use → run `ingest-library`.
- **A fact the graph states is settled.** Use it; never re-derive or
  re-check it. Grow, `ingest-library` and canonize establish facts so
  that no later session has to: the behaviour of a language or a
  library, a best practice, a known bug, a decision, an owner rule. Only
  a fact about the plant's own code can go stale, and only when that
  code moved. Canonize records a code anchor
  (`docs/graph/code-anchor.py --record`), and one comparison at session
  start prints one line. A quiet line: code facts are current. A line
  naming paths: facts about those paths may be stale, the code wins
  there, and the node is fixed in the same change. A not-recorded or
  not-checked line: check the code facts you rely on against the code.
  Settled facts stay settled either way. A worker sees no session-start
  line, so its code facts are current only where its brief carries that
  line saying no code changed. Paths under `docs/graph/` and `.cypress/`
  are the graph and its state, not code.
- **The graph compounds.** Record facts when code gains them, sharp
  edges when they bite, `load_when:` triggers when routing missed. Write
  "not recorded" for any fact, version, or URL you do not have
  (`knowledge-graph`, rule 3).
- **The graph outranks the harness's working style**
  (`context-router.graph-over-harness`). Where the graph's doctrine and
  a harness's default working style differ, follow the graph. A
  harness's safety and permission policy is a boundary, not working
  style, and the graph never overrides it.

Authoring and maintaining what this rule loads is
`skill.knowledge-graph` (`docs/graph/skills/knowledge-graph.md`): read
its node contract once (the `_schema.md` the graph was built from);
dependency leaves are `skill.library-wiki`. Prefer a configured Context7
/ DeepWiki / `llms.txt` MCP server for *fetching* upstream content. If
the project has no graph yet, build one via `adopt-existing` /
`knowledge-graph` first; until then, fall back to reading the README and
the plan-of-record, and say you did.

## The algorithm

### 1. Classify the task in one sentence

Say what kind of work it is before deciding what to read. The four kinds
route differently:

| Kind | Example | Entry |
|---|---|---|
| **Question** | "how does auth work?" | The node that *owns* the fact. Answer with citations. Read code only when the node proves wrong. |
| **Change** | "add a field to X" | The owning subsystem node + its required closure. |
| **Trace** | "why is this endpoint 401-ing?" | Every node on the request/data path. Follow `peers` deliberately — this is the one kind that legitimately crosses them. |
| **Plan** | "rebuild the deploy pipeline" | The plan-of-record + the relevant platform/infra nodes. |

### 2. Route first, then resolve entry nodes

Route the task line before you open anything: take the router
suggestion the host injected for this prompt, or, where no hook
injected one (a hookless host, a spawned child, a task line of your
own), run `python3 docs/graph/graph-lint.py --plan "<task>"`. Its LOAD
set is your entry set with the `requires:` closure already taken; read
it through `--show` (step 3). A `!` notice says the plan is thin, wide
or empty; an empty plan's notice names the next step: a sharper task
line, or the protocol entry nodes (an ungrown plant's include
`protocol.initialize`).

The graph's router index, `docs/graph/index.md` (Tier 1), is the
fallback map, not a first read. Open it only when the router fails,
when a notice leaves the plan empty or wrong, or when the task explores
the graph itself. There, match the task against each node's
`load_when:` triggers. Prefer the most specific match. A task
naming a path resolves to that subsystem's node; a task naming a concept
resolves to the node that `owns` it.

If nothing matches, you have found a gap in the graph. Say so, fall back
to the root node, and note it for the graph's maintainer to fix.

**A standard's match surfaces its standing exceptions.** A `deviation.*`
node (kind `deviation`, `status: standing`; the schema's "Node kinds")
carries the departed-from standard's own name in its `load_when`, so a
task that matches the standard's topic also matches every deliberate
departure from it. Load it with the standard: a standing deviation is
part of the answer and stays settled until its `ends_when` says it stops
applying.

**Watch for aliased names across layers.** When a subsystem answers to
more than one name (a repo or folder name that differs from its product
name, its package/artifact name, and its internal code name), a task
that types one alias can silently fail to match a node keyed to another,
and neither `load_when` matching nor a `grep` sees the miss. The Tier-1
router index must carry an explicit **naming-divergence note** listing
the aliases for each such subsystem, so routing and search see every one
of them. When you hit an unlisted alias, add it to that note in the same
change (like sharpening a `load_when` trigger).

### 3. Take the closure

Load each entry node, then transitively load every node in its
`requires:` list. That much you cannot be correct without. It is small
by construction; if it is not, the graph is mis-modelled and should be
fixed rather than worked around.

Read the routed nodes through
`python3 docs/graph/graph-lint.py --show <id>...`, not the raw files:
for each id it prints a header with the node's path and every pointer
it holds (`requires`, `peers`, `composes`, `delegates_to` as ids;
`artifacts`, `libraries`, `plant_knowledge` as paths), then the body
verbatim. It drops only the keys that are router input, spawn
configuration, or a copy of the body: `load_when`, `routing_triggers`,
`est_tokens`, `tier`, `kind`, `name`, `description`, `prevents`, and the
spawn keys `tools`, `model`, `effort`, `can_delegate`,
`max_spawn_depth`, `command`. Every other key stays in the header, so
no edge and no leaf is lost.

**Whatever else a node lists is a menu** (`context-router.menu`). Open a
leaf, child, link, neighbour or index row a loaded node names only when
its one-line "load when" serves your task, one item at a time, and list
each one you pass over in the skip block (step 5). Only the `requires:`
closure loads in full. A thin parent saves context only if its reader
does not go on to open every leaf it names.

Then, from every loaded `expertise` node, take the composed children the
task names **specifically**: descend into a child when the task uses,
exactly, a term in that child's own vocabulary (its `load_when:`
triggers plus its whole slug) that the parent does not already carry. So
family words sitting on the parent descend nobody, and descent never
folds a prefix the way the router's own entry matching does. A child you
take becomes the parent for its own children, which is the whole of the
recursion. `composes:` is a menu, not a closure: the specialisations the
task is not about stay unread, and you say so (step 5).

A child you turn out to need but that descent did not reach is the same
signal as a `load_when:` that should have matched and didn't. Load it,
say you widened, and sharpen that child's triggers in the same change,
so the next task routes there without you.

### 4. Cross a peer only on purpose

`peers:` are the boundaries you are choosing not to cross. Load a peer
only when the task explicitly crosses into it, and say why. The one
exception is a **trace**: following a request or a message across
subsystems is exactly what `peers` edges are for.

### 5. Declare before you work

Print the resolved set, however small the task. It is the artifact that
lets a reviewer catch a bad load before it becomes a bad change, and the
only record of what you did not read. Declare it in the compact lines
`graph-lint.py --plan` prints, so a route you accept as it stands is
declared by naming it, and a set you changed shows the change:

```
Task: add field <F> to <entity>  [change]
LOAD <n> ~<t>t
<entry node> <path> | <title>
<required node> <path> | <title>
<composed child> <path> | <title> <- composed by <expertise node> on "<term>"
skip (cross only if the task needs it):
 peer of <entry node>: <id>=<path> <id>=<path>
 composed by <expertise node>, no specific term: <id>=<path>
open on demand: <library page, spec or ADR>; the "depth" leaf <expertise node> names
```

One skip block, whatever kept a node out. A peer you chose not
to cross and a specialisation the task never named are the same kind of
record (the boundary, and the reason it held), and a set that lists only
one of them hides the other.

Then, and only then, open source files: only the ones the loaded nodes
name.

### 6. Widen honestly, never silently

If mid-task you discover you need a node you did not load, load it and
say so ("Widening: loading <node>, because the change is not local: …").
Silent widening is the failure this skill prevents. So is stubbornly
working without a node you need in order to look disciplined. Both are
worse than "I was wrong about the boundary."

## Check the route

The graph router is executable, and every session runs it first (the
kernel's FIRST MOVE, and this skill's step 2 above). A spawned worker
runs it through the canonical block every delegation brief embeds
(`docs/graph/templates/prompts/graph-session-bootstrap.md`); this skill
owns only the traversal *algorithm*. When your own reading of the task
resolves a different set than the route, one of you is wrong; usually
a `load_when:` trigger needs sharpening, a cheap permanent fix. That fix
re-ranks every node, not only the one edited: titles and triggers are
both scored text, and a sharper trigger on one node can push a peer out
of a capped result that an earlier fix depended on. Re-run every routing
probe fixed during the session after its last trigger or title edit, not
after each one.

**`--plan` is a keyword heuristic, not an oracle.** It ranks nodes by
weighted term overlap; it does not reason about a request path or a
false premise. Trust it for a single-subject change or question, and as
a floor everywhere. On four kinds of task, trust your own reasoning over
its output:

- **Traces**: the right nodes are the hops on the path, which keyword
  overlap cannot infer.
- **False-premise questions** ("confirm we use X"): the correcting node
  may share no words with the wrong assumption; ask which node would own
  the truth.
- **Policy questions**: these have one owning node; `--plan` may pad the
  set. Prefer the single owner.
- **Compound / multi-topic tasks**: a task description that bundles
  several distinct topics dilutes each topic's distinctive terms below
  the keyword threshold, so the ranking can resolve to the *wrong* node
  and specialist set entirely, beyond a merely partial one. Probe each
  sub-topic separately, or explicitly discount the output for a task you
  know is compound.

## Stopping rules

Stop loading ONLY when one of these is true, because the closure is the
rule:

- The closure is exhausted: `requires:` transitively, plus every
  composed child the task named specifically.
- You can state the change you are about to make and name the contract
  it must not break.
- The next node you would open is a `peer` the task does not cross into,
  or a composed child the task never named.

## Cost discipline

- **Within the loaded scope, retrieve progressively.** The closure names
  the files; read within them from indexes, headings, symbols, and diffs
  to regions, and from excerpts to full files, taking the complete
  source only when exactness demands it. Query order and when one source
  decides a question are the retrieval posture in
  `docs/graph/method/decision-economy.md` ("Every operation serves a
  decision").
- Confirming a path with `ls` or `grep` is fine; reading twenty files to
  build a mental model is the bulk read the knowledge rule replaces with
  the graph.
- A **change** task should load a handful of nodes. If it needs many, it
  is really several tasks; split it and say so.
- A **trace** may legitimately load many nodes, ONLY along its one path.
- **Read a shared convention from the shared node.** When two sibling
  subsystems look near-identical, what they share belongs in a shared
  node. A convention you can infer only by comparing siblings is missing
  from its home, so add it there.

## Residency

Loading minimally decides *which* text enters a session; residency
decides how long it stays. Every text that can enter a session belongs
to exactly one of four classes, placed by the test, not by file type:

| Class | Test | How it is held |
|---|---|---|
| **1. Resident, full** | Every task needs it. | Loaded once at session start, in full. Nothing restates it, per-prompt hooks included. Only the kernel. |
| **2. Resident, pointer** | The model must know it exists before it can know it needs it. | Always visible as one line naming *when* to reach for it; the explanation lives in the body. |
| **3. Once per session** | Some tasks need it, and may need it again. | Protocol and skill bodies. Surfaced when first routed; after that the hook's reminder names it by id on its `seen:` line (open it again only if it is no longer in view), with entry lines only for ids new to the session, until a reset or refresh. |
| **4. Per lookup** | It is consulted for a fact, not followed as a procedure. | Never resident. Reference corpora: read the section, cite, move on. |

An item that fits two classes takes the smaller resident footprint, and
you say why. Dedup applies within one context. A spawned agent starts
empty, so repetition across a subagent spawn is how the brief's
canonical block arrives verbatim. Children are not routed: the
per-prompt hooks inject nothing into a child session or into a turn a
person did not type, so a child routes its own task line as its brief
says. A hook can know what it *surfaced*, never what the model *read*.
How the per-prompt hooks hold to this is the CYPRESS seed's own spec
`SPEC-0003-per-prompt-injection`.

## Reference files

- `docs/graph/skills/knowledge-graph.md`: builds and lints the graph.
- `docs/graph/_schema.md`: the node contract (the adopted copy beside
  the graph; `docs/graph/templates/knowledge-graph/_schema.md` is the
  pristine seed template, fast-forwarded on graft).
- `docs/graph/templates/knowledge-graph/index.md`: the router-index
  template.
- the kernel (`AGENTS.md`): the context-budget rule this skill
  implements.