feat(azure-cost): add App Service optimization guide

[jongio]

Adds an App Service cost optimization reference guide to the azure-cost skill.

Changes

• New services/appservice/azure-app-service.md with optimization rules (stopped apps, empty plans, Premium in dev, idle slots, over-provisioned plans), tier decision matrix, Resource Graph queries, CLI commands, and pricing
• Consolidated service routing in workflow.md into a compact table (Storage + App Service), reducing token usage
• Added 2 vally eval stimuli for App Service cost routing
• Minor trim to azure-storage.md intro and SKILL.md to maintain token budgets

Checklist

• Tests pass locally (cd tests && npm test): vally lint 3/3, build passes, token limits pass
• If modifying skill descriptions: verified routing correctness. App Service cost prompts use explicit cost/savings language to avoid routing to azure-deploy or azure-prepare
• If modifying skill USE FOR / DO NOT USE FOR / PREFER OVER clauses: confirmed no routing regressions

Related Issues

Partial progress on #2524

[Copilot]

Pull request overview

Adds Azure App Service cost optimization coverage to the azure-cost skill by introducing a service-specific reference guide and wiring it into the cost-optimization workflow, with eval stimuli to validate routing.

Changes:

• Added a new App Service optimization reference (azure-app-service.md) and linked it from the skill + workflow.
• Consolidated service-specific routing in the cost-optimization workflow into a compact triggers table (Storage + App Service).
• Added App Service routing stimuli to evals/azure-cost/eval.yaml and trimmed some markdown to maintain token budgets.

Show a summary per file

File	Description
plugin/skills/azure-cost/SKILL.md	Adds App Service to the Service Optimization Guides links and trims some scope/reference entries.
plugin/skills/azure-cost/cost-optimization/workflow.md	Replaces the Storage-only conditional section with a compact service-specific triggers → reference table including App Service.
plugin/skills/azure-cost/cost-optimization/services/storage/azure-storage.md	Minor intro text trim.
plugin/skills/azure-cost/cost-optimization/services/appservice/azure-app-service.md	New App Service cost optimization reference (rules, tier matrix, ARG queries, commands, pricing notes).
evals/azure-cost/eval.yaml	Adds 2 integration routing stimuli for App Service cost prompts.

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 4

[Copilot]

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 7

[Copilot]

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 1

[Copilot]

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 2

[wbreza]

Code Review — PR #2559

Two-model independent review (Claude Opus 4.7 + GPT-5.4). Findings tagged by consensus.

TL;DR

App Service guide is mostly sound (slot billing language and serverfarm/site distinction are correct), but there are a few technical-accuracy issues worth a second look — most notably a KQL query that doesn't enforce the rule it documents, and an "Always On" recommendation that doesn't actually affect App Service billing.

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🔴 Critical (one model)

Workflow bypass — cost data not gathered before recommendations

File: plugin/skills/azure-cost/cost-optimization/workflow.md (Step 1.7 area)

After the workflow.md consolidation, an App Service request can load services/appservice/azure-app-service.md and produce savings recommendations without first executing the mandatory cost-query / bill-breakdown flow in Step 2+. The service guide doesn't restate that requirement either. Consider explicitly re-entering Step 2 after a service guide loads, or restating the bill-breakdown requirement inside the App Service guide.

"Disable Always On" as a cost-saving action

File: plugin/skills/azure-cost/cost-optimization/services/appservice/azure-app-service.md

App Service is billed at the plan level — turning Always On off does not reduce plan charges. Always On is a free per-app toggle that affects cold-start / warm-up behavior, not billing. Recommend removing this from the cost rules list, or reframing it strictly as a perf tradeoff (not an optimization a user will see on their bill).

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🟡 Important

"Stopped App on Paid Plan" KQL doesn't check plan tier (consensus — both reviewers)

File: plugin/skills/azure-cost/cost-optimization/services/appservice/azure-app-service.md

The rule's detection logic says "Site state == Stopped AND plan tier is not Free/Shared", but the query only filters on properties.state =~ 'Stopped' and isnotempty(properties.serverFarmId). It never joins to microsoft.web/serverfarms to inspect sku.tier, so stopped apps on Free/Shared plans (which incur no plan cost) will be returned and incorrectly recommended for deletion/downgrade.

Suggested rewrite:

Resources
| where type =~ 'microsoft.web/sites'
| where properties.state =~ 'Stopped'
| extend planId = tolower(tostring(properties.serverFarmId))
| join kind=inner (
    Resources
    | where type =~ 'microsoft.web/serverfarms'
    | project planId = tolower(id), planSku = tostring(sku.name), planTier = tostring(sku.tier)
  ) on planId
| where planTier !in~ ('Free', 'Shared', 'Dynamic')
| project name, resourceGroup, planSku, planTier

Decision matrix conflates Free and Basic on SLA

File: plugin/skills/azure-cost/cost-optimization/services/appservice/azure-app-service.md (tier decision matrix)

Basic is a paid dedicated tier with a 99.95% SLA, but the matrix row groups "Free / Basic B1" under "No SLA". This materially misstates tier semantics in a rightsizing guide. Split into separate rows, or drop the "No SLA" claim from Basic.

SKILL.md description missing App Service trigger terms

File: plugin/skills/azure-cost/SKILL.md

The top-level skill description doesn't include any App Service / web app / deployment-slot trigger language even though this PR adds an App Service guide and two App Service routing evals. Without those terms in the description, prompts like "how can I save on my App Service plan?" may not reliably route to azure-cost. Consider adding: "App Service cost", "web app spending", "deployment slots", "App Service plan".

Orphan reference file after link removal (consensus — both reviewers)

File: plugin/skills/azure-cost/SKILL.md (removed link)

The PR removes the [SDK: Redis .NET](cost-optimization/sdk/azure-resource-manager-redis-dotnet.md) link from SKILL.md, but the target file still exists on disk and is referenced nowhere else in the skill tree. After merge it ships in the plugin as a dead file. Either delete the file in this PR, or keep the link. If the intent is cleanup, suggest splitting into its own change.

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🟢 Nits

• Premium tier list mismatch — services/appservice/azure-app-service.md: detection row lists ['PremiumV2','PremiumV3'] while the KQL query below includes 'Premium' (v1) too. Align both to the same set.
• Step grouping inconsistency — workflow.md: Storage + App Service are consolidated into a shared step while Redis (1.5) and AKS (1.8) remain separate. Not blocking, just inconsistent.

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What looks good ✅

• Slot-billing language correctly states slots share plan workers (addresses prior reviewer concern).
• serverfarms vs sites distinction is correctly used elsewhere in the guide.
• New eval stimuli follow the existing routing-test pattern.
• Frontmatter and token budgets look compliant.

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Verdict

Comment — content is close to mergeable; the Stopped-Apps KQL, Always On framing, and Basic-SLA row are the highest-value fixes before merge. Author can adjudicate the workflow bypass concern and the orphan SDK file as they see fit.

_{Generated via multi-model code review (Opus 4.7 + GPT-5.4) with cross-model consensus tagging.}