feat(chatd): add provider-native web search tools to chats (#22909)

## What

Adds provider-native web search tools to the chat system. Anthropic,
OpenAI, and Google all offer server-side web search — this wires them up
as opt-in per-model config options using the existing
`ChatModelProviderOptions` JSONB column (no migration).

Web search is **off by default**.

## Config

Set `web_search_enabled: true` in the model config provider options:

```json
{
  "provider_options": {
    "anthropic": {
      "web_search_enabled": true,
      "allowed_domains": ["docs.coder.com", "github.com"]
    }
  }
}
```

Available options per provider:

- **Anthropic**: `web_search_enabled`, `allowed_domains`,
`blocked_domains`
- **OpenAI**: `web_search_enabled`, `search_context_size`
(`low`/`medium`/`high`), `allowed_domains`
- **Google**: `web_search_enabled`

## Backend

- `codersdk/chats.go` — new fields on the per-provider option structs
- `coderd/chatd/chatd.go` — `buildProviderTools()` reads config, creates
`ProviderDefinedTool` entries (uses `anthropic.WebSearchTool()` helper
from fantasy)
- `coderd/chatd/chatloop/chatloop.go` — `ProviderTools` on `RunOptions`,
merged into `Call.Tools`. Provider-executed tool calls skip local
execution. `StreamPartTypeToolResult` with `ProviderExecuted: true` is
accumulated inline (matching fantasy's own agent.go pattern) instead of
post-stream synthesis.
- `coderd/chatd/chatprompt/` — `MarshalToolResult` carries
`ProviderMetadata` through DB persistence so multi-turn round-trips work
(Anthropic needs `encrypted_content` back)

## Frontend

- Source citations render **inline** at the tool-call position (not
bottom-of-message), using `ToolCollapsible` so they look like other tool
cards — collapsed "Searched N results" with globe icon, expand to see
source pills
- Provider-executed tool calls/results are hidden from the normal tool
card UI
- Tool-role messages with only provider-executed results return `null`
(no empty bubble)
- Both persisted (messageParsing.ts) and streaming (streamState.ts)
paths group consecutive `source` parts into a single `{ type: "sources"
}` render block

## Fantasy changes

The fantasy fork (`kylecarbs/fantasy` branch `cj/go1.25`) has the
Anthropic tool code merged in, but will hopefully go upstream from:
https://github.com/charmbracelet/fantasy/pull/163

go.mod

@@ -76,7 +76,7 @@ replace github.com/spf13/afero => github.com/aslilac/afero v0.0.0-20250403163713
 // 1) Adds thinking effort to Anthropic provider
 // 2) Downgraded to Go 1.25 due to issue with Windows CI
 // https://github.com/kylecarbs/fantasy/compare/main...kylecarbs:fantasy:cj/go1.25
-replace charm.land/fantasy => github.com/kylecarbs/fantasy v0.0.0-20260225152134-45ae0791c21f
+replace charm.land/fantasy => github.com/kylecarbs/fantasy v0.0.0-20260311152049-8eff3573caec
 
 replace github.com/charmbracelet/anthropic-sdk-go => github.com/kylecarbs/anthropic-sdk-go v0.0.0-20260223140439-63879b0b8dab
 
@@ -91,7 +91,7 @@ require (
 	github.com/aquasecurity/trivy-iac v0.8.0
 	github.com/armon/circbuf v0.0.0-20190214190532-5111143e8da2
 	github.com/awalterschulze/gographviz v2.0.3+incompatible
-	github.com/aws/smithy-go v1.24.1
+	github.com/aws/smithy-go v1.24.2
 	github.com/bramvdbogaerde/go-scp v1.6.0
 	github.com/briandowns/spinner v1.23.0
 	github.com/cakturk/go-netstat v0.0.0-20200220111822-e5b49efee7a5
@@ -214,7 +214,7 @@ require (
 	golang.org/x/text v0.34.0
 	golang.org/x/tools v0.42.0
 	golang.org/x/xerrors v0.0.0-20240903120638-7835f813f4da
-	google.golang.org/api v0.267.0
+	google.golang.org/api v0.269.0
 	google.golang.org/grpc v1.79.1
 	google.golang.org/protobuf v1.36.11
 	gopkg.in/DataDog/dd-trace-go.v1 v1.74.0
@@ -260,20 +260,20 @@ require (
 	github.com/apparentlymart/go-textseg/v15 v15.0.0 // indirect
 	github.com/armon/go-radix v1.0.1-0.20221118154546-54df44f2176c // indirect
 	github.com/atotto/clipboard v0.1.4 // indirect
-	github.com/aws/aws-sdk-go-v2 v1.41.1
-	github.com/aws/aws-sdk-go-v2/config v1.32.9
-	github.com/aws/aws-sdk-go-v2/credentials v1.19.9 // indirect
-	github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.18.17 // indirect
+	github.com/aws/aws-sdk-go-v2 v1.41.3
+	github.com/aws/aws-sdk-go-v2/config v1.32.11
+	github.com/aws/aws-sdk-go-v2/credentials v1.19.11 // indirect
+	github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.18.19 // indirect
 	github.com/aws/aws-sdk-go-v2/feature/rds/auth v1.6.2
-	github.com/aws/aws-sdk-go-v2/internal/configsources v1.4.17 // indirect
-	github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.7.17 // indirect
-	github.com/aws/aws-sdk-go-v2/internal/ini v1.8.4 // indirect
-	github.com/aws/aws-sdk-go-v2/service/internal/accept-encoding v1.13.4 // indirect
-	github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.13.17 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/configsources v1.4.19 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.7.19 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/ini v1.8.5 // indirect
+	github.com/aws/aws-sdk-go-v2/service/internal/accept-encoding v1.13.6 // indirect
+	github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.13.19 // indirect
 	github.com/aws/aws-sdk-go-v2/service/ssm v1.60.1 // indirect
-	github.com/aws/aws-sdk-go-v2/service/sso v1.30.10 // indirect
-	github.com/aws/aws-sdk-go-v2/service/ssooidc v1.35.14 // indirect
-	github.com/aws/aws-sdk-go-v2/service/sts v1.41.6 // indirect
+	github.com/aws/aws-sdk-go-v2/service/sso v1.30.12 // indirect
+	github.com/aws/aws-sdk-go-v2/service/ssooidc v1.35.16 // indirect
+	github.com/aws/aws-sdk-go-v2/service/sts v1.41.8 // indirect
 	github.com/aymanbagabas/go-osc52/v2 v2.0.1 // indirect
 	github.com/aymerick/douceur v0.2.0 // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
@@ -456,7 +456,7 @@ require (
 	google.golang.org/appengine v1.6.8 // indirect
 	google.golang.org/genproto v0.0.0-20260217215200-42d3e9bedb6d // indirect
 	google.golang.org/genproto/googleapis/api v0.0.0-20260217215200-42d3e9bedb6d // indirect
-	google.golang.org/genproto/googleapis/rpc v0.0.0-20260217215200-42d3e9bedb6d // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20260226221140-a57be14db171 // indirect
 	gopkg.in/ini.v1 v1.67.1 // indirect
 	howett.net/plist v1.0.0 // indirect
 	kernel.org/pub/linux/libs/security/libcap/psx v1.2.77 // indirect
@@ -468,6 +468,7 @@ require github.com/coder/clistat v1.2.1
 require github.com/SherClockHolmes/webpush-go v1.4.0
 
 require (
+	github.com/aws/aws-sdk-go-v2/internal/v4a v1.4.17 // indirect
 	github.com/charmbracelet/colorprofile v0.4.1 // indirect
 	github.com/charmbracelet/x/cellbuf v0.0.15 // indirect
 	github.com/go-json-experiment/json v0.0.0-20251027170946-4849db3c2f7e // indirect
@@ -518,18 +519,17 @@ require (
 	github.com/aquasecurity/jfather v0.0.8 // indirect
 	github.com/aquasecurity/trivy v0.61.1-0.20250407075540-f1329c7ea1aa // indirect
 	github.com/aquasecurity/trivy-checks v1.12.2-0.20251219190323-79d27547baf5 // indirect
-	github.com/aws/aws-sdk-go-v2/aws/protocol/eventstream v1.7.4 // indirect
-	github.com/aws/aws-sdk-go-v2/internal/v4a v1.4.17 // indirect
+	github.com/aws/aws-sdk-go-v2/aws/protocol/eventstream v1.7.5 // indirect
 	github.com/aws/aws-sdk-go-v2/service/internal/checksum v1.9.8 // indirect
 	github.com/aws/aws-sdk-go-v2/service/internal/s3shared v1.19.17 // indirect
 	github.com/aws/aws-sdk-go-v2/service/s3 v1.96.0 // indirect
-	github.com/aws/aws-sdk-go-v2/service/signin v1.0.5 // indirect
+	github.com/aws/aws-sdk-go-v2/service/signin v1.0.7 // indirect
 	github.com/bahlo/generic-list-go v0.2.0 // indirect
 	github.com/bgentry/go-netrc v0.0.0-20140422174119-9fd32a8b3d3d // indirect
 	github.com/bits-and-blooms/bitset v1.24.4 // indirect
 	github.com/buger/jsonparser v1.1.1 // indirect
 	github.com/cenkalti/backoff/v5 v5.0.3 // indirect
-	github.com/charmbracelet/anthropic-sdk-go v0.0.0-20251024181547-21d6f3d9a904 // indirect
+	github.com/charmbracelet/anthropic-sdk-go v0.0.0-20260223140439-63879b0b8dab // indirect
 	github.com/charmbracelet/x/exp/slice v0.0.0-20250904123553-b4e2667e5ad5 // indirect
 	github.com/charmbracelet/x/json v0.2.0 // indirect
 	github.com/clipperhouse/displaywidth v0.9.0 // indirect
@@ -611,7 +611,7 @@ require (
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
 	go.yaml.in/yaml/v4 v4.0.0-rc.3 // indirect
 	golang.org/x/telemetry v0.0.0-20260209163413-e7419c687ee4 // indirect
-	google.golang.org/genai v1.47.0 // indirect
+	google.golang.org/genai v1.49.0 // indirect
 	gopkg.in/warnings.v0 v0.1.2 // indirect
 	k8s.io/utils v0.0.0-20250820121507-0af2bda4dd1d // indirect
 	mvdan.cc/gofumpt v0.8.0 // indirect