Delta Tracking

Rather than rewriting specs when things change, Canon tracks changes through status transitions and hidden HTML comments embedded in the spec markdown.

How It Works

Each spec section has a hidden status comment that the agent manages:

## 3. Idempotency Layer
<!-- canon:system:idempotency status:done -->
<!-- canon:ticket:jira:PAY-142 -->

All payment endpoints must support idempotency keys...

### 3.1 Key Generation
<!-- canon:system:key-gen status:done -->
<!-- canon:ticket:jira:PAY-143 -->
<!-- canon:realized-in:PR#412 src/payments/keys.ts -->

- [x] Generate UUID v4 idempotency keys on client
- [x] Store keys in Redis with 24h TTL

Comment Types

Canon uses three types of hidden HTML comments:

Status Comments

<!-- canon:system:<section-id> status:<status> -->

Tracks the current status of a section. Valid statuses:

Status	Meaning
draft	Initial state — requirements not yet finalized
todo	Ready for implementation
in_progress	Work has started
done	All acceptance criteria verified against code
blocked	Waiting on a dependency (optionally: blocked:TICKET-ID)
deprecated	No longer relevant

Ticket Links

<!-- canon:ticket:<system>:<ticket-id> -->

Links a spec section to a ticket in an external system:

<!-- canon:ticket:jira:PAY-142 -->
<!-- canon:ticket:linear:ID-301 -->
<!-- canon:ticket:github:42 -->

Realization Evidence

<!-- canon:realized-in:PR#<number> <file>:<lines> -->

The critical addition — the agent writes this when it verifies that code actually implements the spec section, not just when a ticket is closed:

<!-- canon:realized-in:PR#412 src/payments/keys.ts:42-60 -->

Status Transitions

Statuses typically flow in one direction:

draft → todo → in_progress → done
                    ↓
                 blocked → in_progress → done

The agent auto-transitions statuses based on code evidence:

• todo → in_progress: When a PR references this section
• in_progress → done: When all acceptance criteria are realized
• Any → blocked: When a dependency is unresolved

PMs can manually set any status. The deprecated status is terminal — the agent stops tracking the section.

Why Hidden Comments?

Hidden HTML comments are invisible when rendering the markdown in GitHub, editors, or documentation sites. This means:

1. Clean reading experience — No metadata clutter in the spec
2. Git-friendly — Comments are just text, so they diff and merge normally
3. Tool-agnostic — Any markdown renderer handles them correctly
4. Human-editable — Engineers can manually fix comments if needed

The agent manages these comments automatically. Engineers rarely need to touch them directly.

Related

• Reference: Spec Format — formal syntax for all comment types, frontmatter, and ACs
• Guide: Writing Specs — how to write specs with proper status lifecycle
• Concept: Living Specs — the feedback loop that drives status transitions
• Concept: Spec Coverage — how realization evidence feeds into coverage metrics
• Reference: CLI — canon start and canon done for manual transitions
• Reference: MCP Tools — update_section_status and add_realization for agent use