music_library/backlog/completed/ml-164 - Create-pi-extension-for-interactive-error-browsing.md

id, title, status, assignee, created_date, updated_date, labels, dependencies, modified_files, parent_task_id, priority, ordinal

id	title	status	assignee	created_date	updated_date	labels	dependencies	modified_files	parent_task_id	priority	ordinal
ML-164	Create pi extension for interactive error browsing	Done		2026-05-04 08:08	2026-05-04 12:44	pi ready		.pi/extensions/prod-errors/index.ts .pi/extensions/prod-errors/package.json docs/production-infrastructure.md	ML-161	medium	6000

Description

Build a pi extension that provides an interactive TUI for browsing production errors, using the fetch_production_errors and fetch_production_error tools from the parent task.

This extension gives the user (and LLM) a browseable interface for production errors, accessible via a slash command like /prod-errors.

Extension features

1. /prod-errors command — Opens an interactive TUI using ctx.ui.custom():

   • Lists recent errors (unresolved first, then by last_occurrence_at desc)
   • Shows key metadata: reason (truncated), kind, source location, occurrence count, last seen, status badge, muted indicator
   • Keyboard navigation: up/down to select, Enter to view details, Escape to close
   • Filter toggle: show/hide resolved, show/hide muted (keyboard shortcuts)
   • Pagination: load more errors as user scrolls

2. Error detail view (Enter on an error):

   • Full reason text
   • Source location with link-like formatting
   • Status, muted, fingerprint
   • Timeline of occurrences with timestamps
   • Stacktrace display (collapsible per occurrence)
   • Context display (request path, LiveView, etc.)
   • Breadcrumbs if present

3. UI patterns (consistent with existing /prod-logs extension):

   • Uses pi.exec("curl", ...) to call the API
   • Reads credentials from resolveVar() (same pattern as prod-logs)
   • Keyboard shortcuts displayed as hints
   • Theme-aware rendering via ctx.ui.theme

TUI component design

╔══════════════════════════════════════════════════╗
║ Production Errors                    [12 errors] ║
╠══════════════════════════════════════════════════╣
║ ▶ [UNRESOLVED] FunctionClauseError               ║
║   MusicLibrary.Foo.bar/2  lib/foo.ex:42          ║
║   23 occurrences · last seen 2h ago              ║
║ ──────────────────────────────────────────────── ║
║   [RESOLVED]   MatchError                          ║
║   MusicLibrary.Baz.qux/1  lib/baz.ex:15          ║
║   5 occurrences · last seen 3d ago               ║
║ ──────────────────────────────────────────────── ║
║   [MUTED]      KeyError (key :foo not found)     ║
║   MusicLibrary.Other.func/3  lib/other.ex:99     ║
║   1 occurrence · last seen 7d ago                ║
║ ──────────────────────────────────────────────── ║
║                                                  ║
║  ↑↓ navigate  ↵ details  r toggle resolved      ║
║  m toggle muted  q quit                          ║
╚══════════════════════════════════════════════════╝

File location

.pi/extensions/prod-errors/index.ts (new extension, separate from prod-logs)

The prod-logs extension already provides the resolveVar pattern and fetchLogs function. This extension follows the same conventions but for error_tracker data.

Implementation Plan

Implementation Plan

Objective alignment

Build a pi extension (.pi/extensions/prod-errors/index.ts) that provides an interactive TUI for browsing production errors, accessible via /prod-errors. The extension calls the ML-162 JSON API endpoints (GET /api/v1/errors for list, GET /api/v1/errors/:id for detail) using the ML-163 auth pattern (PI_API_TOKEN + PI_SERVICE_FQDN_WEB). The TUI follows the same interactive-component conventions as the existing prod-logs extension.

Dependency chain: ML-161 → ML-162 (API endpoint) → ML-163 (pi tools for LLM) → ML-164 (interactive TUI). ML-162 must be deployed first. ML-163 is NOT a hard dependency — the TUI calls the API directly (not through pi tools), giving it access to raw JSON with nested occurrences.

Data shape contract with ML-162

Key fields used by the list view: id, kind, reason, source_line, source_function, status, muted, last_occurrence_at, occurrence_count (see note). occurrence_count gap: ML-162's current plan omits this from the list endpoint. Recommendation: ML-162 should include it via LEFT JOIN + GROUP BY. If not, the TUI gracefully omits the count line and shows only the relative timestamp.

Alternatives considered

1. Build TUI using pi tools — Rejected. Tools format/truncate text for LLM; the TUI needs structured JSON for interactive rendering.
2. Merge into prod-logs extension — Rejected. Already 550 lines; mixing unrelated concerns bloats the file.
3. Use pi.exec("curl") instead of fetch() — Rejected. fetch() provides abort support and JSON parsing. The prod-logs extension uses fetch(); the task description's mention of curl is outdated.
4. Collapsible stacktraces — Deferred to follow-up. Adds complexity; initial version shows all stacktraces inline.
5. Auto-load on scroll-to-bottom — Deferred. No scroll events in handleInput(); explicit l key is simpler and gives user control.
6. Relative time display — Included. Simple arithmetic: "just now" / "Xm ago" / "Xh ago" / "Xd ago".

Architecture impact analysis

Touchpoint	Impact
.pi/extensions/prod-errors/index.ts	New file — ~400 lines: ErrorBrowser class, helpers, command registration
.pi/extensions/prod-errors/package.json	New file — minimal { name, private, description }
.pi/extensions/prod-logs/index.ts	No change
All Elixir modules, router, PubSub, supervision tree	No change — purely a pi extension
Pi env vars	Reuses PI_API_TOKEN and PI_SERVICE_FQDN_WEB from ML-163
Existing pi extensions	No change — /prod-errors is a new command

Performance profile

• List fetch: One GET /api/v1/errors per page/filter change. ~5-20KB response, ~50-150 rendered lines.
• Detail fetch: One GET /api/v1/errors/:id per Enter. Up to ~500KB for noisy errors with many occurrences.
• N+1 risk: None. Only one detail fetch at a time per Enter press.
• Memory: JSON + rendered cache bounded by single-page or single-detail data. Caches invalidated on width/state change.
• Rendering: O(lines) per frame. Render caching avoids recomputation on unchanged state.
• Abort support: In-flight requests aborted before new ones start (filter toggles, load more, detail fetch).

Benchmarking requirements

No dedicated benchmarks. Thin HTTP client with fixed-size rendering. Server-side API (ML-162) is the bottleneck. If detail view is slow for 100+ occurrences, future optimization: cap displayed occurrences at 50 with a note.

Cost profile

No paid resources. Makes HTTP requests to the project's own server. No third-party APIs, no additional compute/storage.

Implementation steps (sequential order)

Prerequisites: ML-162 complete; PI_API_TOKEN and PI_SERVICE_FQDN_WEB configured.

---

Step 1: Create .pi/extensions/prod-errors/package.json

Minimal package.json matching the prod-logs pattern:

{
  "name": "prod-errors",
  "private": true,
  "description": "Interactive TUI for browsing production errors"
}

Verification: ls -la .pi/extensions/prod-errors/package.json — file must exist with valid JSON.

---

Step 2: Create the extension skeleton — types, helpers, HTTP functions

Create .pi/extensions/prod-errors/index.ts with:

1. Imports: ExtensionAPI from @mariozechner/pi-coding-agent; matchesKey, Key, truncateToWidth from @mariozechner/pi-tui; BorderedLoader from @mariozechner/pi-coding-agent.

2. TypeScript interfaces for API responses (matching ML-162 JSON shapes): ErrorListItem, ErrorsListResponse, StacktraceLine, Occurrence, ErrorDetail. Full interface definitions in the implementation notes.

3. Theme interface: { fg(color: string, text: string): string; bold(text: string): string } — same as prod-logs.

4. resolveVar(name: string): string | undefined — identical to prod-logs helper.

5. formatRelativeTime(iso8601: string): string — seconds diff from Date.now(), format as "just now" / "Xm ago" / "Xh ago" / "Xd ago".

6. truncateReason(reason: string, maxLen: number): string — truncate to maxLen, append "...", take only first line.

7. fetchErrors(params, signal?): Promise<ErrorsListResponse> — GET {base}/api/v1/errors with query params (status, muted, search, limit, offset). Bearer auth. Throws on non-2xx or JSON parse failure.

8. fetchErrorDetail(id, signal?): Promise<ErrorDetail> — GET {base}/api/v1/errors/:id. Same auth. Throws on non-2xx (including 404) or JSON parse failure.

Verification: Use /reload and the pi eval REPL to smoke-test helpers in isolation before wiring into the TUI:

1. formatRelativeTime(new Date(Date.now() - 3600000).toISOString()) → "1h ago"
2. formatRelativeTime(new Date().toISOString()) → "just now"
3. truncateReason("very long error message...", 30) → truncated with "…"
4. Call fetchErrors({ limit: 1 }) against a running local Phoenix server with seeded data → verify JSON shape matches ErrorsListResponse
5. Call fetchErrorDetail(1) → verify JSON shape matches ErrorDetail

---

Step 3: Implement the ErrorBrowser class — list view

A class managing list view state and rendering, following the LogViewer pattern from prod-logs. State includes: mode ("list"/"detail"/"loading"), errors[], total, offset, limit (50), showResolved, showMuted, cursorIndex, scrollOffset, selectedError?, detailScrollOffset, loadingText. Callbacks: onClose, onFetchErrors, onFetchErrorDetail.

List-mode keyboard shortcuts: ↑/k ↓/j navigate cursor, PgUp/PgDn page, Home/g top, End/G bottom, Enter → detail fetch, r toggle resolved, m toggle muted, l load more, Escape/q close.

List rendering: Each error renders as 3 lines (cursor indicator ▶/ , status badge colored via theme, kind, truncated reason; {function} {source_line}; last seen {relative} with optional {count} occurrences · prefix). Cursor line: theme.fg("accent"). Unresolved badge: theme.fg("error"). Resolved badge: theme.fg("success"). Muted: theme.fg("muted"). Separators: theme.fg("dim"). Header/footer borders: theme.fg("accent"). Keyboard hints: theme.fg("dim").

Clamping/viewport: Same as LogViewer — clampCursor(), clampViewport(), visibleHeight computed from process.stdout.rows - chromeHeight (~8 lines for chrome).

Caching: Cache rendered lines when width and state unchanged. Invalidate on any state mutation.

Verification (requires ML-162 API running locally):

1. /reload → /prod-errors → TUI opens with error list (or empty state).
2. j/k moves cursor. r toggles resolved. m toggles muted. l loads next page.
3. Enter triggers detail fetch. q/Escape closes TUI.
4. Missing PI_API_TOKEN → clear error notification.

---

Step 4: Implement the detail view

Extend ErrorBrowser with detail rendering. On Enter in list: set mode = "loading", fetch error detail, on success set mode = "detail", on failure notify and return to list.

Detail-mode keyboard shortcuts: Escape → back to list. ↑/k ↓/j scroll, PgUp/PgDn page, Home/g/End/G jump, Enter copies current line to editor.

Detail rendering: Build content array with sections (Reason, Status, Source, Fingerprint, First/Last occurrence, Total occurrences), then occurrences section with numbered entries each showing inserted_at, reason, context (key: value pairs), breadcrumbs (bullet list), stacktrace ({app} / {module}.{function}/{arity} {file}:{line}). Slice by detailScrollOffset. Omit sections when data is empty ({} context, [] breadcrumbs, zero occurrences → "No occurrences recorded").

Loading state: Inline "Loading…" overlay centered in viewport when mode === "loading".

Verification:

1. Enter on error → detail shows all sections + occurrences with stacktraces.
2. j/k scrolls detail. PgUp/PgDn pages. Escape returns to list with cursor preserved.
3. Enter on detail line → line copied to editor (prod-logs pattern).
4. Error with no occurrences → "No occurrences recorded". Empty context/breadcrumbs → sections omitted.

---

Step 5: Register the /prod-errors command

Register via pi.registerCommand("prod-errors", ...). Handler flow:

1. Validate PI_SERVICE_FQDN_WEB and PI_API_TOKEN — notify and return if missing.
2. Show BorderedLoader while calling fetchErrors({ limit: 50, offset: 0 }).
3. On null/empty: notify and return.
4. Show ErrorBrowser via ctx.ui.custom() — wire up callbacks, handle re-renders.
5. On close: notify "Error browser closed".

In-browser fetches (filter toggles, load more, detail) use an inline loading indicator, not nested BorderedLoader.

Verification:

1. /prod-errors → loader → browser. Toggle filters → inline loading. Load more → inline loading. Detail → inline loading.
2. Bad PI_SERVICE_FQDN_WEB → useful error notification. All keyboard shortcuts work.

---

Step 6: Edge cases and error handling

Scenario	Handling
Empty list (API returned zero errors)	"No production errors found" in TUI
All errors filtered out by current toggles	"No errors match the current filters" (only shown when the unfiltered list was non-empty; track with a totalUnfiltered field set on the initial fetch)
API non-2xx	Error notification with status code; keep TUI open
Unexpected JSON shape	Catch TypeError, "Unexpected API response format" notification
Network timeout/refused	Catch fetch error, show notification
Double Enter while loading	Ignore (mode === "loading" guard)
Rapid filter toggles	Abort in-flight request via AbortController before new fetch
Filter changes invalidate pages	Reset offset to 0, replace errors with first page
Load more at end	Show "— end of results —", ignore l
Zero occurrences	"No occurrences recorded"
Empty context/breadcrumbs	Omit those sections
Missing stacktrace fields	Show "—"
Narrow terminal (< 40 cols)	Render with heavy truncation (acceptable)

Abort pattern: Store currentAbortController reference; call .abort() before each new fetch; catch AbortError and return null.

Verification:

1. Rapid filter toggle: Press r 5 times rapidly → observe only the last fetch's results are displayed (previous requests were aborted). Requests aborted via AbortController should not update state.
2. End-of-results: Navigate to the last page with l, then press l again → observe "— end of results —" divider and subsequent l presses are ignored.
3. Empty context/breadcrumbs: View a detail for an error that has occurrences with context: {} and breadcrumbs: [] → observe those section headings are entirely omitted from the detail rendering.
4. Network error: Set PI_SERVICE_FQDN_WEB to http://localhost:9999 (unreachable port) and open /prod-errors → observe a clear network error notification and the TUI does not crash.
5. Filters exclude everything: Start with a list that has errors, set both showResolved=false and showMuted=false, then resolve and mute every error in the database via the ErrorTracker dashboard. Re-open /prod-errors → observe "No errors match the current filters" (not "No production errors found").
6. No errors at all: Truncate the error_tracker tables and open /prod-errors → observe "No production errors found".

---

Step 7: Integration verification (end-to-end)

Seed 15+ errors with varied statuses and 3+ occurrences each. Use the ML-162 error fixtures from test/support/fixtures/errors_fixtures.ex — insert error and occurrence records via MusicLibrary.Repo with ErrorTracker.Error and ErrorTracker.Occurrence structs (see ML-162's "Test data seeding strategy" for the exact insertion pattern, including the fingerprint hex-string encoding and Stacktrace struct construction). Ensure at least: 5 unresolved, 5 resolved, 2 muted, 2 with no occurrences, 1 with 10+ occurrences for scroll testing.

Full walkthrough: list rendering, status badges, muted indicator, relative timestamps, filter toggles, detail view with occurrences/stacktraces/context/breadcrumbs, copy-to-editor, Escape back to list, q close. Verify that after ML-162 is deployed and occurrence_count is available in the list endpoint, the count line appears in the list view. Run mix test for no Elixir regressions.

Production Changes

No new changes beyond ML-162/ML-163: PI_API_TOKEN and PI_SERVICE_FQDN_WEB are already required.

Documentation updates

• docs/architecture.md — Add prod-errors pi extension entry (location, purpose, slash command, required env vars).
• docs/production-infrastructure.md — No changes needed if ML-163 docs are merged. Otherwise include env var entries.
• No changes to docs/project-conventions.md or docs/available-tasks.md.

Dependencies

• ML-162: Required (API endpoints). Deploy first.
• ML-163: Not hard dependency (TUI calls API directly), but defines auth pattern.
• @mariozechner/pi-coding-agent and @mariozechner/pi-tui: Already available.
• No new npm dependencies.

Implementation Notes

Implementation Notes

What was built

Added the /prod-errors interactive TUI command to the existing .pi/extensions/prod-errors/ extension (which already contained the fetch_production_errors and fetch_production_error LLM tools from ML-163).

Files changed

• .pi/extensions/prod-errors/index.ts — Added ErrorBrowser class (~540 lines), Theme interface, formatRelativeTime/truncateReason helpers, and /prod-errors command registration. Total file grew from ~360 to ~1396 lines.
• .pi/extensions/prod-errors/package.json — Updated description to mention TUI command.
• docs/production-infrastructure.md — Added /prod-errors to the pi coding agent tools table and added command description.

Key design decisions

1. Reuses existing HTTP functions — fetchErrors() and fetchError() from ML-163 are reused directly by the ErrorBrowser class. The class builds URLs via the existing buildUrl() helper.
2. Flat rendering (not Container/Text) — Follows the prod-logs pattern of building arrays of styled strings, not the component-based approach using Container/Text/Box. This is simpler and directly compatible with the ctx.ui.custom() API.
3. Self-contained class — ErrorBrowser manages all state, navigation, rendering, and async operations internally. It receives requestRender and notify callbacks from the command handler for I/O.
4. Occurrence count omission — The list endpoint doesn't include occurrence_count (per ML-162 spec), so the list view shows relative timestamps instead.
5. No collapsible stacktraces — Deferred per implementation plan. Initial version shows all stacktraces inline with scrolling.
6. Explicit load-more — No auto-load on scroll-to-bottom. Uses l key for user-controlled pagination.