---
name: propagate-design-change
description: "When a GDD is revised, scans all ADRs and the traceability index to identify which architectural decisions are now potentially stale. Produces a change impact report and guides the user through resolution."
argument-hint: "[path/to/changed-gdd.md]"
user-invocable: true
allowed-tools: Read, Glob, Grep, Write, Bash
agent: technical-director
---

# Propagate Design Change

When a GDD changes, architectural decisions written against it may no longer be
valid. This skill finds every affected ADR, compares what the ADR assumed against
what the GDD now says, and guides the user through resolution.

**Usage:** `/propagate-design-change design/gdd/combat-system.md`

---

## 1. Validate Argument

A GDD path argument is **required**. If missing, fail with:
> "Usage: `/propagate-design-change design/gdd/[system].md`
> Provide the path to the GDD that was changed."

Verify the file exists. If not, fail with:
> "[path] not found. Check the path and try again."

---

## 2. Read the Changed GDD

Read the current GDD in full.

---

## 3. Read the Previous Version

Run git to get the previous committed version:

```bash
git show HEAD:design/gdd/[filename].md
```

If the file has no git history (new file), report:
> "No previous version in git — this appears to be a new GDD, not a revision.
> Nothing to propagate."

If git returns the previous version, do a conceptual diff:
- Identify sections that changed (new rules, removed rules, modified formulas,
  changed acceptance criteria, changed tuning knobs)
- Identify sections that are unchanged
- Produce a change summary:

```
## Change Summary: [GDD filename]
Date of revision: [today]

Changed sections:
- [Section name]: [what changed — new rule, removed rule, formula modified, etc.]

Unchanged sections:
- [Section name]

Key changes affecting architecture:
- [Change 1 — likely to affect ADRs]
- [Change 2]
```

---

## 4. Load Architecture Inputs

Read all ADRs in `docs/architecture/`:
- For each ADR, read the full file
- Extract the "GDD Requirements Addressed" table
- Note which GDD documents and requirement IDs each ADR references

Read `docs/architecture/architecture-traceability.md` if it exists.

Report: "Loaded [N] ADRs. [M] reference [gdd filename]."

---

## 5. Impact Analysis

For each ADR that references the changed GDD:

Compare the ADR's "GDD Requirements Addressed" entries against the changed sections
of the GDD. For each referenced requirement:

1. **Locate the requirement** in the current GDD — does it still exist?
2. **Compare**: What did the GDD say when the ADR was written vs. what it says now?
3. **Assess the ADR decision**: Is the architectural decision still valid?

Classify each affected ADR as one of:

| Status | Meaning |
|--------|---------|
| ✅ **Still Valid** | The GDD change doesn't affect what this ADR decided |
| ⚠️ **Needs Review** | The GDD change may affect this ADR — human judgment needed |
| 🔴 **Likely Superseded** | The GDD change directly contradicts what this ADR assumed |

For each affected ADR, produce an impact entry:

```
### ADR-NNNN: [title]
Status: [Still Valid / Needs Review / Likely Superseded]

What the ADR assumed about this GDD:
  "[relevant quote from the ADR's GDD Requirements Addressed section]"

What the GDD now says:
  "[relevant quote from the current GDD]"

Assessment:
  [Explanation of whether the ADR decision is still valid, and why]

Recommended action:
  [Keep as-is | Review and update | Mark Superseded and write new ADR]
```

---

## 6. Present Impact Report

Present the full impact report to the user before asking for any action. Format:

```
## Design Change Impact Report
GDD: [filename]
Date: [today]
Changes detected: [N sections changed]
ADRs referencing this GDD: [M]

### Not Affected
[ADRs referencing this GDD whose decisions remain valid]

### Needs Review ([count])
[ADRs that may need updating]

### Likely Superseded ([count])
[ADRs whose assumptions are now contradicted]
```

---

## 7. Resolution Workflow

For each ADR marked "Needs Review" or "Likely Superseded", ask the user what to do:

Ask for each ADR in turn:
> "ADR-NNNN ([title]) — [status]. What would you like to do?"
> Options:
> - "Mark Superseded (I'll write a new ADR)" — updates ADR status line to `Superseded by: [pending]`
> - "Update in place (minor revision)" — opens the ADR for editing; note what to revise
> - "Keep as-is (the change doesn't actually affect this decision)"
> - "Skip for now (revisit later)"

For ADRs marked **Superseded**:
- Update the ADR's Status field: `Superseded by ADR-[next number] (pending — see change-impact-[date]-[system].md)`
- Ask: "May I update the status in [ADR filename]?"

---

## 8. Update Traceability Index

If `docs/architecture/architecture-traceability.md` exists:
- Add the changed GDD requirements to the "Superseded Requirements" table:

```markdown
## Superseded Requirements
| Date | GDD | Requirement | Changed To | ADRs Affected | Resolution |
|------|-----|-------------|------------|---------------|------------|
| [date] | [gdd] | [old requirement text] | [new requirement text] | ADR-NNNN | [Superseded/Updated/Valid] |
```

Ask: "May I update the traceability index?"

---

## 9. Output Change Impact Document

Ask: "May I write the change impact report to `docs/architecture/change-impact-[date]-[system-slug].md`?"

The document contains:
- The change summary from step 3
- The full impact analysis from step 5
- Resolution decisions made in step 7
- List of ADRs that need to be written or updated

If user approved: Verdict: **COMPLETE** — change impact report saved.
If user declined: Verdict: **BLOCKED** — user declined write.

---

## 10. Follow-Up Actions

Based on the resolution decisions, suggest:

- **ADRs marked Superseded**: "Run `/architecture-decision [title]` to write the
  replacement ADR. Then re-run `/propagate-design-change` to verify coverage."
- **ADRs to update in place**: List the specific fields to update in each ADR
- **If many ADRs affected**: "Run `/architecture-review` after all ADRs are updated
  to verify the full traceability matrix is still coherent."

---

## Collaborative Protocol

1. **Read silently** — compute the full impact before presenting anything
2. **Show the full report first** — let the user see the scope before asking for action
3. **Ask per-ADR** — don't batch decisions; each affected ADR may need different treatment
4. **Ask before writing** — always confirm before modifying any file
5. **Non-destructive** — never delete ADR content; only add "Superseded by" notes
