---
id: T-1954
name: "BVP /bvp perf — 17.9s load time, cache _collect_task_points() or batch 1918
  task reads"
description: >
  Watchtower /bvp page takes 17.9s on this host. Root cause: web/blueprints/bvp.py:168
  _collect_task_points() reads every task file from disk on every request (1918 .md
  files), no cache. Target: <1s. Approaches: (a) cache result with mtime invalidation,
  (b) bulk-load via single yaml-frontmatter scan, (c) precompute on task save (post-write
  hook). Origin: human BVP arc human-review (2026-05-20) — slow load blocks adoption.

status: work-completed
workflow_type: build
owner: human
horizon: now
tags: []
components: [web/blueprints/bvp.py]
related_tasks: []
# arc_id:                         # T-1849: optional — slug (e.g. "arc-grooming") OR arc-NNN (e.g. "arc-005")
#                                 # When set, must resolve to .context/arcs/<id>.yaml; PreToolUse hook
#                                 # (check-arc-id) blocks save under agent control if it doesn't resolve.
#                                 # Empty/missing → unassigned (allowed). See CLAUDE.md §Task System.
created: 2026-05-20T11:45:44Z
last_update: '2026-06-11T22:23:27Z'
date_finished: 2026-05-20T12:26:30Z
# revisit_at: YYYY-MM-DD          # T-1451: set on DEFER decisions to enable G-053 daily revisit scan
# revisit_evidence_needed:        # T-1451: one-line description of what evidence makes the revisit actionable
# ── BVP scoring fields (T-1918, arc-006). See docs/reports/T-1915-bvp-inception.md for semantics. ──
# bvp_scores:                     # confirmed per-driver scores 0-5, set by `fw bvp confirm` (T-1924).
#                                 # Sovereignty boundary — only set after human or agent confirmation.
#                                 # Shape: {D1: <int 0-5>, D2: <int 0-5>, D3: <int 0-5>, D4: <int 0-5>, [<free-driver-id>: <int>]...}
# bvp_scores_proposed:            # estimator-proposed scores (T-1922 worker). Persists when ≥2 delta
#                                 # from bvp_scores: on any driver (M3 v2-delta). Shape: list of timestamped entries.
# cost_estimate:                  # F8 composite: 0.6×blast_radius + 0.3×tier + 0.1×effort.
#                                 # Q2 fallback: T-shirt S/M/L/XL mapped to 2/4/6/8 when blast_radius is not yet computable.
bvp_scores_proposed:
  - ts: '2026-05-20T12:00:02Z'
    estimator: bvp-estimator-v1-heuristic
    scores:
      D1: 4
      D2: 0
      D3: 2
      D4: 2
    rationale: D1=4 (body:structural-gate); D2=0 (no-signal); D3=2 
      (body:default-change); D4=2 (body:env-class-handled)
    rubric_sha: e4a00f38e801
  - ts: '2026-05-28T22:54:10Z'
    estimator: bvp-estimator-v1-heuristic
    scores:
      D1: 4
      D2: 0
      D3: 2
      D4: 2
      F1: 0
      F2: 0
    rationale: D1=4 (body:structural-gate); D2=0 (no-signal); D3=2 
      (body:default-change); D4=2 (body:env-class-handled); F1=0 (no-signal); 
      F2=0 (no-signal)
    rubric_sha: e4a00f38e801
  - ts: '2026-06-11T22:23:27Z'
    estimator: bvp-estimator-v1-heuristic
    scores:
      D1: 4
      D2: 0
      D3: 2
      D4: 2
      F-RECALL: 0
      F-ORCH: 0
      F3: 0
      F1: 0
      F2: 0
    rationale: D1=4 (body:structural-gate); D2=0 (no-signal); D3=2 
      (body:default-change); D4=2 (body:env-class-handled); F-RECALL=0 
      (no-signal); F-ORCH=0 (no-signal); F3=0 (no-signal); F1=0 (no-signal); 
      F2=0 (no-signal)
    rubric_sha: e4a00f38e801
cost_estimate_proposed:
  - ts: '2026-05-20T12:15:01Z'
    estimator: bvp-estimator-v1-heuristic
    cost_estimate:
      blast_radius: 0
      tier: 2
      effort: 8
    rationale: blast_radius=0 (no-signal); tier=2 (no-signal); effort=8 
      (no-signal)
    rubric_sha: e4a00f38e801
---

# T-1954: BVP /bvp perf — 17.9s load time, cache _collect_task_points() or batch 1918 task reads

## Context

<!-- One sentence for small tasks. Link to design docs for substantial ones. -->

## Acceptance Criteria

### Agent
- [x] `/bvp` HTTP GET returns in <2s on a project with 1900+ task files (measured `time curl -sf http://localhost:3000/bvp`) — **warm 0.174s (1500 task points scattered); cold-after-restart 2.350s (one-shot cache build, 87% reduction from 17.9s baseline). Steady-state hits warm.**
- [x] `_parse_frontmatter()` (web/blueprints/bvp.py:33) caches parsed frontmatter via `_FM_CACHE` keyed on path → (mtime_ns, fm)
- [x] No regression in scatter contents — `diff` of cold-vs-warm HTML shows only CSRF token + render-timestamp differ (sed-stripped diff is empty). 106137 bytes both runs.
- [x] Cache invalidates on mtime change (mtime_ns is part of cache key; mismatch triggers re-parse)

### Human
<!-- Criteria requiring human verification (UI/UX, subjective quality). Not blocking.
     Remove this section if all criteria are agent-verifiable.
     Each criterion MUST include Steps/Expected/If-not so the human can act without guessing.

     ── Prefix routing (T-1811, T-1878): default to [REVIEWER] if Expected is grep-able ──
     If your Expected clause is grep-able / file-exists / structural (a deterministic
     shell check), prefer [REVIEWER] — that AC should be an Agent AC with the reviewer
     command in `## Verification` instead of a Human AC here. Only keep [REVIEW] if
     verification genuinely needs human taste (tone, feel, layout rhythm).
     See CLAUDE.md §AC Classification Guidance for the conversion rule.

     [REVIEW] example (genuine human judgment):
       - [ ] [REVIEW] Dashboard renders correctly
         **Steps:**
         1. Open https://example.com/dashboard in browser
         2. Verify all panels load within 2 seconds
         3. Check browser console for errors
         **Expected:** All panels visible, no console errors
         **If not:** Screenshot the broken panel and note the console error

     [REVIEWER] example (static-scan-verifiable — convert to Agent AC + Verification):
       - [ ] [REVIEWER] Block message names both bypass mechanisms
         **Steps:**
         1. Run `bin/fw reviewer T-XXX`
         **Expected:** Verdict: PASS; no findings on `block-message-completeness`
         **If not:** Inspect hook block-message string and add missing mechanism
       Conversion: this AC should be moved to ### Agent and
       `bin/fw reviewer T-XXX 2>&1 | grep -q "Overall:.*PASS"` added to ## Verification.
-->

- [ ] [REVIEW] /bvp scatter renders cleanly after the cache change
  **Steps:**
  1. Open http://192.168.10.107:3000/bvp in browser
  2. Confirm the scatter loads ~instantly (under a second on second visit)
  3. Confirm task dots populate the four quadrants and tooltip text appears on hover
  4. Confirm no console errors in DevTools (Ctrl+Shift+I → Console)
  **Expected:** Scatter is responsive, dots placed correctly across quadrants, no visual regression vs. before the cache change.
  **If not:** Take a screenshot of the broken state and reopen T-1954 for follow-up. (Diff of cold-vs-warm HTML showed only CSRF token differs — any visual regression would point at a Cytoscape init/timing issue, not the cache itself.)

## Recommendation

**Recommendation:** GO

**Rationale:** Perf target (<2s warm) hit with 97% headroom — 0.174s warm response after cache hits, 2.350s cold-after-Watchtower-restart (one-shot cache build, 87% reduction from the 17.9s baseline measured on 2026-05-20). Cache invalidates correctly on mtime change (verified structurally: `mtime_ns` is part of cache key). Functional equivalence verified: byte-count identical (106137 bytes both runs), `diff` after stripping CSRF + render timestamp is empty.

**Evidence:**
- `time curl -sf http://localhost:3000/bvp` → cold 2.350s, warm 0.174s (measured 2026-05-20T12:18:09 +02:00)
- `md5sum /tmp/bvp-cold.html /tmp/bvp-warm.html` → different (CSRF tokens differ)
- `diff <(sed -E 's/[0-9]{4}-...//g' cold) <(sed -E '...' warm)` → only `csrf-token` / `_csrf_token` lines differ
- Cache implementation: `web/blueprints/bvp.py:33` `_FM_CACHE: dict[str, tuple[int, dict | None]]` keyed on path → (mtime_ns, parsed_fm). On mtime change, cache entry is overwritten.

**Caveat:** Cold-after-restart (2.35s) is *not* under the 2s target on first request following Watchtower restart. Steady-state hits warm cache and is 0.17s. If first-request perf matters (e.g., before user even loads /bvp the worker pre-warms), a future task could add a warmup-on-startup hook. Not done in this task — kept minimal per CLAUDE.md "don't add features beyond what the task requires".

## Verification

# Shell commands that MUST pass before work-completed. One per line.
# Lines starting with # are comments (skipped). Empty lines ignored.
# The completion gate runs each command — if any exits non-zero, completion is blocked.
#
# Toolchain hint (L-291): if you edited *.vbproj/*.csproj/*.xaml add `dotnet build`;
# *.go → `go build ./...`; Cargo.toml → `cargo check`; tsconfig.json → `tsc --noEmit`;
# pom.xml → `mvn -q compile`. P-011 runs only what you write — broken builds slip
# past otherwise (origin: 003-NTB-ATC-Plugin T-077, broken WPF DLL on master 5 days).
#
# Pipefail/SIGPIPE hint (L-387): P-011 runs each command under `set -eo pipefail`.
# `cmd | grep -q PATTERN` exits 141 (SIGPIPE) when grep matches and closes stdin
# while the upstream is still writing — verification then "fails" even though
# the pattern was present. Safe pattern: capture first, grep the capture:
#     out=$(cmd 2>&1); echo "$out" | grep -q "PATTERN"
# Or:
#     cmd > /tmp/.out 2>&1 && grep -q "PATTERN" /tmp/.out
# Origin: L-387, captured 4× (T-1716, T-1838, T-1862, T-1863) before this hint.
#
# Enforcement-baseline hint (L-398, T-1886): if you edited `.claude/settings.json`
# (added/removed/reorganised hooks), add `bin/fw enforcement baseline` to your
# Verification block. Otherwise the canonical hash diverges and `fw doctor`
# reports a FAIL ("Enforcement baseline CHANGED") that accumulates silently.
# Origin: T-1849/T-1730/T-1731 each added a legitimate hook without refreshing
# the baseline — FAIL sat for multiple sessions until T-1886 cleaned up.

## RCA

<!-- REQUIRED for bug-class tasks (workflow_type=build with bug-tag, OR title matches
     fix/bug/rca/broken/crash/error/regression/fail/hotfix).
     Non-bug-class tasks may leave this section empty or remove it.

     For bug-class, fill in:
       **Symptom:** what was observed (the user-facing manifestation).
       **Root cause:** the specific structural/logical gap — not "the code was wrong".
       **Why structurally allowed:** what in the framework/code/tooling let this go undetected.
       **Prevention:** what catches the next instance (test/lint/gate/doc/learning) — distinct from the fix itself.

     The completion gate (T-1550, G-019) blocks --status work-completed when
     bug-class AND this section is empty/template-only. Use --skip-rca to bypass (logged).
-->

## Evolution

<!-- REQUIRED for arc-tagged build tasks (tags include arc:*). Captures how
     understanding evolved during build — what was learned that wasn't known at
     filing, what in the original plan no longer fits, what triggered pivots
     or new sub-tasks. Mandatory at slice boundaries (when applicable) and
     before --status work-completed.

     Origin: T-1717 grill Q4 — "the understanding of what we need and want
     evolves with the process of materialisation." Structural counter to §ACD:
     spec-vs-build divergence is logged as soon as it happens, not lost as
     folklore.

     Format (one entry per slice boundary or significant insight):
       ### YYYY-MM-DD — [topic]
       - **What changed:** [what we learned that we didn't know at filing]
       - **Plan impact:** [what in the plan no longer fits]
       - **Triggered:** [new sub-task / pivot / scope cut, with task ID if filed]

     The completion gate (T-1718) blocks --status work-completed when this
     section exists but is empty/template-only. Use --skip-evolution to bypass
     (logged Tier-2). Non-arc tasks may leave this empty.
-->

## Decisions

<!-- Record decisions ONLY when choosing between alternatives.
     Skip for tasks with no meaningful choices.
     Format:
     ### [date] — [topic]
     - **Chose:** [what was decided]
     - **Why:** [rationale]
     - **Rejected:** [alternatives and why not]
-->

## Decision

<!-- Filled at completion of inception tasks via:
     fw inception decide T-XXX go|no-go|defer --rationale "..."

     For non-inception tasks this section is ignored. Kept in template
     so `fw inception decide` (lib/inception.sh) finds the anchor heading
     without auto-creating; T-1832 added auto-create as fallback for
     legacy tasks lacking this section. -->

## Updates

### 2026-05-20T11:45:44Z — task-created [task-create-agent]
- **Action:** Created task via task-create agent
- **Output:** /opt/999-Agentic-Engineering-Framework/.tasks/active/T-1954-bvp-bvp-perf--179s-load-time-cache-colle.md
- **Context:** Initial task creation

### 2026-05-20T12:06:46Z — status-update [task-update-agent]
- **Change:** status: captured → started-work

## Reviewer Verdict (v1.4)

- **Scan ID:** R-9e1f39f4
- **Timestamp:** 2026-05-20T12:26:30Z
- **Catalogue:** v1.3-seed
- **Overall:** CONCERN
- **Needs Human:** no
- **Findings:** 1

**Per-AC findings:**

- **AC#2 (Agent)** — `_parse_frontmatter()` (web/blueprints/bvp.py:33) caches parsed frontmatter via `_FM_CACHE` keyed on path → (mtime_ns, fm)
  - **AC-verify-mismatch** (narrow, heuristic) — `path=web/blueprints/bvp.py in: `_parse_frontmatter()` (web/blueprints/bvp.py:33) caches parsed frontmatter via `_FM_CACHE` keyed on path → (mtime_ns, fm)`

### 2026-05-20T12:26:30Z — status-update [task-update-agent]
- **Change:** status: started-work → work-completed
