diff --git a/src/main/github/client.test.ts b/src/main/github/client.test.ts
index 4b5f1375aa8..eef3aace0e7 100644
--- a/src/main/github/client.test.ts
+++ b/src/main/github/client.test.ts
@@ -178,6 +178,7 @@ import {
   getPullRequestPushTarget,
   mergePR,
   resolveReviewThread,
+  setPRCommentReaction,
   setPRAutoMerge,
   updatePRState,
   updatePRTitle,
@@ -4082,6 +4083,113 @@ describe('GitHub GraphQL rate-limit guard', () => {
     )
   })
 
+  it('returns GraphQL reaction subjects and viewer state for PR comments', async () => {
+    getOwnerRepoMock.mockResolvedValueOnce({ owner: 'acme', repo: 'widgets' })
+    ghExecFileAsyncMock
+      .mockResolvedValueOnce({
+        stdout: JSON.stringify({
+          data: {
+            repository: {
+              pullRequest: {
+                comments: {
+                  nodes: [
+                    {
+                      id: 'IC_1',
+                      databaseId: 10,
+                      author: { login: 'octo', avatarUrl: '', __typename: 'User' },
+                      body: 'Issue comment',
+                      createdAt: '2026-04-01T00:00:00Z',
+                      url: 'https://example.test/issue-comment',
+                      reactionGroups: [
+                        {
+                          content: 'THUMBS_UP',
+                          viewerHasReacted: true,
+                          reactors: { totalCount: 2 }
+                        }
+                      ]
+                    }
+                  ]
+                },
+                reviewThreads: {
+                  nodes: [
+                    {
+                      id: 'PRRT_1',
+                      isResolved: false,
+                      line: 4,
+                      startLine: null,
+                      originalLine: 4,
+                      originalStartLine: null,
+                      comments: {
+                        nodes: [
+                          {
+                            id: 'PRRC_1',
+                            databaseId: 11,
+                            author: { login: 'reviewer', avatarUrl: '', __typename: 'User' },
+                            body: 'Inline comment',
+                            createdAt: '2026-04-01T00:01:00Z',
+                            url: 'https://example.test/review-comment',
+                            path: 'src/app.ts',
+                            reactionGroups: [
+                              {
+                                content: 'EYES',
+                                viewerHasReacted: false,
+                                reactors: { totalCount: 1 }
+                              }
+                            ]
+                          }
+                        ]
+                      }
+                    }
+                  ]
+                }
+              }
+            }
+          }
+        })
+      })
+      .mockResolvedValueOnce({ stdout: '[]' })
+      .mockResolvedValueOnce({ stdout: '[]' })
+
+    const comments = await getPRComments('/repo-root', 7, {
+      prRepo: { owner: 'acme', repo: 'widgets', host: 'github.com' }
+    })
+
+    expect(comments).toEqual([
+      expect.objectContaining({
+        id: 10,
+        reactionSubjectId: 'IC_1',
+        reactions: [{ content: '+1', count: 2, viewerHasReacted: true }]
+      }),
+      expect.objectContaining({
+        id: 11,
+        reactionSubjectId: 'PRRC_1',
+        reactions: [{ content: 'eyes', count: 1, viewerHasReacted: false }]
+      })
+    ])
+  })
+
+  it('adds and removes PR comment reactions through GraphQL', async () => {
+    getOwnerRepoMock.mockResolvedValue({ owner: 'acme', repo: 'widgets' })
+    ghExecFileAsyncMock.mockResolvedValue({ stdout: '{}', stderr: '' })
+
+    await expect(setPRCommentReaction('/repo-root', 'IC_1', '+1', true)).resolves.toBe(true)
+    await expect(setPRCommentReaction('/repo-root', 'PRRC_1', 'eyes', false)).resolves.toBe(true)
+
+    expect(ghExecFileAsyncMock).toHaveBeenNthCalledWith(
+      1,
+      expect.arrayContaining(['subjectId=IC_1', 'content=THUMBS_UP']),
+      expect.any(Object)
+    )
+    expect(ghExecFileAsyncMock.mock.calls[0]?.[0].join(' ')).toContain('addReaction')
+    expect(ghExecFileAsyncMock).toHaveBeenNthCalledWith(
+      2,
+      expect.arrayContaining(['subjectId=PRRC_1', 'content=EYES']),
+      expect.any(Object)
+    )
+    expect(ghExecFileAsyncMock.mock.calls[1]?.[0].join(' ')).toContain('removeReaction')
+    expect(noteRateLimitSpendMock).toHaveBeenCalledTimes(2)
+  })
+
   it('uses explicit PR repo for merge and title mutations', async () => {
     ghExecFileAsyncMock
       .mockResolvedValueOnce({
diff --git a/src/main/github/client.ts b/src/main/github/client.ts
index 07472e5c096..c1a9d0e3891 100644
--- a/src/main/github/client.ts
+++ b/src/main/github/client.ts
@@ -12,6 +12,7 @@ import type {
   PRCheckDetail,
   PRCheckRunDetails,
   GitHubCommentResult,
+  GitHubReactionContent,
   GitHubPRReviewCommentInput,
   PRComment,
   GitHubViewer,
@@ -110,7 +111,11 @@ import {
   mapPRState,
   deriveCheckStatus
 } from './mappers'
-import { mapGraphQLReactionGroups, type GitHubGraphQLReactionGroup } from './comment-reactions'
+import {
+  mapGraphQLReactionGroups,
+  toGraphQLReactionContent,
+  type GitHubGraphQLReactionGroup
+} from './comment-reactions'
 import {
   getRateLimit,
   noteRepositoryRateLimitSpend,
@@ -4117,6 +4122,7 @@ query($owner: String!, $repo: String!, $pr: Int!) {
           originalStartLine
           comments(first: 100) {
             nodes {
+              id
               databaseId
               author { __typename login avatarUrl(size: 48) }
               body
@@ -4125,6 +4131,7 @@ query($owner: String!, $repo: String!, $pr: Int!) {
               path
               reactionGroups {
                 content
+                viewerHasReacted
                 reactors {
                   totalCount
                 }
@@ -4135,6 +4142,7 @@ query($owner: String!, $repo: String!, $pr: Int!) {
       }
       comments(first: 100) {
         nodes {
+          id
           databaseId
           author { __typename login avatarUrl(size: 48) }
           body
@@ -4142,6 +4150,7 @@ query($owner: String!, $repo: String!, $pr: Int!) {
           url
           reactionGroups {
             content
+            viewerHasReacted
             reactors {
               totalCount
             }
@@ -4255,6 +4264,7 @@ export async function getPRComments(
         originalStartLine: number | null
         comments: {
           nodes: {
+            id: string
             databaseId: number
             author: { __typename?: string; login: string; avatarUrl: string } | null
             body: string
@@ -4266,6 +4276,7 @@ export async function getPRComments(
         }
       }
       type GQLIssueComment = {
+        id: string
         databaseId: number
         author: { __typename?: string; login: string; avatarUrl: string } | null
         body: string
@@ -4295,6 +4306,7 @@ export async function getPRComments(
             createdAt: c.createdAt,
             url: c.url,
             isBot: c.author?.__typename === 'Bot',
+            reactionSubjectId: c.id,
             reactions: mapGraphQLReactionGroups(c.reactionGroups)
           })
         )
@@ -4313,6 +4325,7 @@ export async function getPRComments(
               createdAt: c.createdAt,
               url: c.url,
               isBot: c.author?.__typename === 'Bot',
+              reactionSubjectId: c.id,
               reactions: mapGraphQLReactionGroups(c.reactionGroups),
               path: c.path,
               threadId: thread.id,
@@ -4393,6 +4406,62 @@ export async function getPRComments(
   }
 }
 
+export async function setPRCommentReaction(
+  repoPath: string,
+  reactionSubjectId: string,
+  content: GitHubReactionContent,
+  reacted: boolean,
+  connectionId?: string | null,
+  prRepo?: GitHubApiRepository | null,
+  localGitOptions: LocalGitExecOptions = {}
+): Promise<boolean> {
+  const mutation = reacted ? 'addReaction' : 'removeReaction'
+  const query = `mutation($subjectId: ID!, $content: ReactionContent!) {
+    ${mutation}(input: { subjectId: $subjectId, content: $content }) {
+      subject { id }
+    }
+  }`
+  const { ownerRepo, ghOptions } = await resolveGitHubRepoExecution(
+    repoPath,
+    prRepo,
+    connectionId,
+    localGitOptions
+  )
+  if (!ownerRepo) {
+    return false
+  }
+  const guard = repositoryRateLimitGuard(ownerRepo, 'graphql', ghOptions)
+  if (guard.blocked) {
+    console.warn(
+      `${mutation} skipped: GitHub GraphQL rate limit nearly exhausted (${guard.remaining}/${guard.limit})`
+    )
+    return false
+  }
+  await acquire()
+  try {
+    noteRepositoryRateLimitSpend(ownerRepo, 'graphql', 1, ghOptions)
+    await ghExecFileAsync(
+      [
+        'api',
+        'graphql',
+        '-f',
+        `query=${query}`,
+        '-f',
+        `subjectId=${reactionSubjectId}`,
+        '-f',
+        `content=${toGraphQLReactionContent(content)}`
+      ],
+      ghOptions
+    )
+    return true
+  } catch (err) {
+    console.warn(`${mutation} failed:`, err)
+    return false
+  } finally {
+    release()
+  }
+}
+
 /**
  * Mark or unmark a PR file as viewed via GitHub's GraphQL API.
  */
diff --git a/src/main/github/comment-reactions.test.ts b/src/main/github/comment-reactions.test.ts
index 4478214076f..4c0366fda3f 100644
--- a/src/main/github/comment-reactions.test.ts
+++ b/src/main/github/comment-reactions.test.ts
@@ -1,19 +1,19 @@
 import { describe, expect, it } from 'vitest'
 
-import { mapGraphQLReactionGroups } from './comment-reactions'
+import { mapGraphQLReactionGroups, toGraphQLReactionContent } from './comment-reactions'
 
 describe('mapGraphQLReactionGroups', () => {
   it('normalizes GraphQL reaction groups into GitHub comment reactions', () => {
     expect(
       mapGraphQLReactionGroups([
-        { content: 'EYES', reactors: { totalCount: 1 } },
-        { content: 'THUMBS_UP', reactors: { totalCount: 2 } },
+        { content: 'EYES', reactors: { totalCount: 1 }, viewerHasReacted: false },
+        { content: 'THUMBS_UP', reactors: { totalCount: 2 }, viewerHasReacted: true },
         { content: 'HEART', reactors: { totalCount: 0 } },
         { content: 'UNKNOWN', reactors: { totalCount: 9 } }
       ])
     ).toEqual([
-      { content: '+1', count: 2 },
-      { content: 'eyes', count: 1 }
+      { content: '+1', count: 2, viewerHasReacted: true },
+      { content: 'eyes', count: 1, viewerHasReacted: false }
     ])
   })
 
@@ -22,4 +22,9 @@ describe('mapGraphQLReactionGroups', () => {
       undefined
     )
   })
+
+  it('maps REST reaction content to the GraphQL enum', () => {
+    expect(toGraphQLReactionContent('+1')).toBe('THUMBS_UP')
+    expect(toGraphQLReactionContent('hooray')).toBe('HOORAY')
+  })
 })
diff --git a/src/main/github/comment-reactions.ts b/src/main/github/comment-reactions.ts
index d93ae551c26..1bb831f30ca 100644
--- a/src/main/github/comment-reactions.ts
+++ b/src/main/github/comment-reactions.ts
@@ -13,6 +13,7 @@ type GitHubGraphQLReactionContent =
 export type GitHubGraphQLReactionGroup = {
   content?: string | null
   reactors?: { totalCount?: number | null } | null
+  viewerHasReacted?: boolean | null
 }
 
 const GRAPHQL_REACTION_CONTENT: Record<GitHubGraphQLReactionContent, GitHubReactionContent> = {
@@ -37,10 +38,27 @@ const REACTION_ORDER: GitHubReactionContent[] = [
   'eyes'
 ]
 
+const REACTION_CONTENT_TO_GRAPHQL: Record<GitHubReactionContent, GitHubGraphQLReactionContent> = {
+  '+1': 'THUMBS_UP',
+  '-1': 'THUMBS_DOWN',
+  laugh: 'LAUGH',
+  confused: 'CONFUSED',
+  heart: 'HEART',
+  hooray: 'HOORAY',
+  rocket: 'ROCKET',
+  eyes: 'EYES'
+}
+
+export function toGraphQLReactionContent(
+  content: GitHubReactionContent
+): GitHubGraphQLReactionContent {
+  return REACTION_CONTENT_TO_GRAPHQL[content]
+}
+
 export function mapGraphQLReactionGroups(
   groups?: GitHubGraphQLReactionGroup[] | null
 ): GitHubReaction[] | undefined {
-  const counts = new Map<GitHubReactionContent, number>()
+  const reactionsByContent = new Map<GitHubReactionContent, GitHubReaction>()
   for (const group of groups ?? []) {
     const content =
       group.content && group.content in GRAPHQL_REACTION_CONTENT
@@ -50,12 +68,20 @@ export function mapGraphQLReactionGroups(
     if (!content || count <= 0) {
       continue
     }
-    counts.set(content, (counts.get(content) ?? 0) + count)
+    const existing = reactionsByContent.get(content)
+    const viewerHasReacted = Boolean(existing?.viewerHasReacted || group.viewerHasReacted)
+    reactionsByContent.set(content, {
+      content,
+      count: (existing?.count ?? 0) + count,
+      ...(existing?.viewerHasReacted !== undefined || group.viewerHasReacted != null
+        ? { viewerHasReacted }
+        : {})
+    })
   }
 
   const reactions = REACTION_ORDER.flatMap((content) => {
-    const count = counts.get(content) ?? 0
-    return count > 0 ? [{ content, count }] : []
+    const reaction = reactionsByContent.get(content)
+    return reaction ? [reaction] : []
   })
   return reactions.length > 0 ? reactions : undefined
 }
diff --git a/src/main/ipc/github.test.ts b/src/main/ipc/github.test.ts
index bbd26f84d6a..c137c399480 100644
--- a/src/main/ipc/github.test.ts
+++ b/src/main/ipc/github.test.ts
@@ -22,6 +22,7 @@ const {
   getPRChecksMock,
   getPRCheckDetailsMock,
   getPRCommentsMock,
+  setPRCommentReactionMock,
   resolveReviewThreadMock,
   setPRFileViewedMock,
   addPRReviewCommentMock,
@@ -64,6 +65,7 @@ const {
   getPRChecksMock: vi.fn(),
   getPRCheckDetailsMock: vi.fn(),
   getPRCommentsMock: vi.fn(),
+  setPRCommentReactionMock: vi.fn(),
   resolveReviewThreadMock: vi.fn(),
   setPRFileViewedMock: vi.fn(),
   addPRReviewCommentMock: vi.fn(),
@@ -123,6 +125,7 @@ vi.mock('../github/client', () => ({
   getPRChecks: getPRChecksMock,
   getPRCheckDetails: getPRCheckDetailsMock,
   getPRComments: getPRCommentsMock,
+  setPRCommentReaction: setPRCommentReactionMock,
   resolveReviewThread: resolveReviewThreadMock,
   setPRFileViewed: setPRFileViewedMock,
   addPRReviewComment: addPRReviewCommentMock,
@@ -212,6 +215,7 @@ describe('registerGitHubHandlers', () => {
     getPRChecksMock.mockReset()
     getPRCheckDetailsMock.mockReset()
     getPRCommentsMock.mockReset()
+    setPRCommentReactionMock.mockReset()
     resolveReviewThreadMock.mockReset()
     setPRFileViewedMock.mockReset()
     addPRReviewCommentMock.mockReset()
@@ -907,6 +911,7 @@ describe('registerGitHubHandlers', () => {
     getPRChecksMock.mockResolvedValue([])
     getPRCheckDetailsMock.mockResolvedValue(null)
     getPRCommentsMock.mockResolvedValue([])
+    setPRCommentReactionMock.mockResolvedValue(true)
     resolveReviewThreadMock.mockResolvedValue(true)
     setPRFileViewedMock.mockResolvedValue(true)
     addPRReviewCommentReplyMock.mockResolvedValue({ ok: true })
@@ -964,6 +969,13 @@ describe('registerGitHubHandlers', () => {
       prRepo,
       noCache: true
     })
+    await handlers['gh:setPRCommentReaction'](null, {
+      repoPath: '/workspace/repo',
+      reactionSubjectId: ' IC_1 ',
+      content: '+1',
+      reacted: true,
+      prRepo
+    })
     await handlers['gh:resolveReviewThread'](null, {
       repoPath: '/workspace/repo',
       threadId: 'thread-1',
@@ -1124,6 +1136,15 @@ describe('registerGitHubHandlers', () => {
       null,
       localGitOptions
     )
+    expect(setPRCommentReactionMock).toHaveBeenCalledWith(
+      '/workspace/repo',
+      'IC_1',
+      '+1',
+      true,
+      null,
+      prRepo,
+      localGitOptions
+    )
     expect(resolveReviewThreadMock).toHaveBeenCalledWith(
       '/workspace/repo',
       'thread-1',
diff --git a/src/main/ipc/github.ts b/src/main/ipc/github.ts
index 6fcc53bab71..91cfc94f061 100644
--- a/src/main/ipc/github.ts
+++ b/src/main/ipc/github.ts
@@ -13,6 +13,7 @@ import type {
   GitHubPRRefreshCandidate,
   GitHubPRRefreshEnqueueResult,
   GitHubPRRefreshReason,
+  GitHubReactionContent,
   PRRefreshOutcome,
   GitHubPRFile
 } from '../../shared/types'
@@ -39,6 +40,7 @@ import {
   getPRChecks,
   getPRCheckDetails,
   getPRComments,
+  setPRCommentReaction,
   resolveReviewThread,
   setPRFileViewed,
   addPRReviewComment,
@@ -667,6 +669,36 @@ export function registerGitHubHandlers(store: Store, stats: StatsCollector): voi
     }
   )
 
+  ipcMain.handle(
+    'gh:setPRCommentReaction',
+    (
+      _event,
+      args: {
+        repoPath: string
+        repoId?: string | null
+        sourceContext?: TaskSourceContext | null
+        reactionSubjectId: string
+        content: GitHubReactionContent
+        reacted: boolean
+        prRepo?: GitHubOwnerRepo | null
+      }
+    ) => {
+      const repo = assertRegisteredRepo(args, store)
+      if (!args.reactionSubjectId?.trim()) {
+        return false
+      }
+      return setPRCommentReaction(
+        repo.path,
+        args.reactionSubjectId.trim(),
+        args.content,
+        args.reacted,
+        repoConnectionId(repo),
+        args.prRepo ?? null,
+        ...localGitOptionArgs(store, repo)
+      )
+    }
+  )
+
   ipcMain.handle(
     'gh:resolveReviewThread',
     async (
diff --git a/src/main/runtime/orca-runtime.ts b/src/main/runtime/orca-runtime.ts
index 526acea823b..33de03a4a09 100644
--- a/src/main/runtime/orca-runtime.ts
+++ b/src/main/runtime/orca-runtime.ts
@@ -228,6 +228,7 @@ import type {
   GitHubPullRequestStateUpdate,
   GitHubPRFile,
   GitHubPRReviewCommentInput,
+  GitHubReactionContent,
   GitLabIssueUpdate,
   GitLabMRInlineCommentInput,
   GitLabProjectRef,
@@ -591,6 +592,7 @@ import {
   getPRCheckDetails,
   rerunPRChecks,
   getPRComments,
+  setPRCommentReaction,
   getIssue,
   resolveReviewThread,
   setPRFileViewed,
@@ -20147,6 +20149,25 @@ export class OrcaRuntimeService {
     )
   }
 
+  async setRepoPRCommentReaction(
+    repoSelector: string,
+    reactionSubjectId: string,
+    content: GitHubReactionContent,
+    reacted: boolean,
+    prRepo?: GitHubOwnerRepo | null
+  ): Promise<Awaited<ReturnType<typeof setPRCommentReaction>>> {
+    const repo = await this.resolveRepoSelector(repoSelector)
+    return setPRCommentReaction(
+      repo.path,
+      reactionSubjectId,
+      content,
+      reacted,
+      repo.connectionId ?? null,
+      prRepo ?? null,
+      ...this.getLocalGitExecutionOptionArgs(repo)
+    )
+  }
+
   async getRepoPRFileContents(
     repoSelector: string,
     args: {
diff --git a/src/main/runtime/rpc/methods/github.test.ts b/src/main/runtime/rpc/methods/github.test.ts
index 06cc04d917e..0a283b52072 100644
--- a/src/main/runtime/rpc/methods/github.test.ts
+++ b/src/main/runtime/rpc/methods/github.test.ts
@@ -219,6 +219,31 @@ describe('github RPC methods', () => {
     expect(response).toMatchObject({ ok: true, result: [] })
   })
 
+  it('sets a PR comment reaction on the runtime server', async () => {
+    const runtime = {
+      getRuntimeId: () => 'test-runtime',
+      setRepoPRCommentReaction: vi.fn().mockResolvedValue(true)
+    } as unknown as OrcaRuntimeService
+    const dispatcher = new RpcDispatcher({ runtime, methods: GITHUB_METHODS })
+
+    const response = await dispatcher.dispatch(
+      makeRequest('github.setPRCommentReaction', {
+        repo: 'repo-1',
+        reactionSubjectId: 'IC_1',
+        content: 'heart',
+        reacted: true,
+        prRepo: { owner: 'acme', repo: 'widgets', host: 'github.acme.test' }
+      })
+    )
+
+    expect(runtime.setRepoPRCommentReaction).toHaveBeenCalledWith('repo-1', 'IC_1', 'heart', true, {
+      owner: 'acme',
+      repo: 'widgets',
+      host: 'github.acme.test'
+    })
+    expect(response).toMatchObject({ ok: true, result: true })
+  })
+
   it('fetches PR file contents on the runtime server', async () => {
     const runtime = {
       getRuntimeId: () => 'test-runtime',
diff --git a/src/main/runtime/rpc/methods/github.ts b/src/main/runtime/rpc/methods/github.ts
index 858d22b72bb..ed715e4e0e8 100644
--- a/src/main/runtime/rpc/methods/github.ts
+++ b/src/main/runtime/rpc/methods/github.ts
@@ -73,6 +73,13 @@ const PullRequest = RepoSelector.extend({
   prRepo: SlugRepo.nullable().optional()
 })
 
+const PRCommentReaction = RepoSelector.extend({
+  reactionSubjectId: requiredString('Missing reaction subject ID'),
+  content: z.enum(['+1', '-1', 'laugh', 'confused', 'heart', 'hooray', 'rocket', 'eyes']),
+  reacted: z.boolean(),
+  prRepo: SlugRepo.nullable().optional()
+})
+
 const PullRequestChecks = PullRequest.extend({
   headSha: OptionalString
 })
@@ -459,6 +466,18 @@ export const GITHUB_METHODS: RpcMethod[] = [
         noCache: params.noCache
       })
   }),
+  defineMethod({
+    name: 'github.setPRCommentReaction',
+    params: PRCommentReaction,
+    handler: async (params, { runtime }) =>
+      runtime.setRepoPRCommentReaction(
+        params.repo,
+        params.reactionSubjectId,
+        params.content,
+        params.reacted,
+        params.prRepo ?? null
+      )
+  }),
   defineMethod({
     name: 'github.prFileContents',
     params: PullRequestFileContents,
diff --git a/src/preload/api-types.ts b/src/preload/api-types.ts
index bc6abd8cc03..87c8fce5901 100644
--- a/src/preload/api-types.ts
+++ b/src/preload/api-types.ts
@@ -226,6 +226,7 @@ import type {
   MarkdownDocument,
   FloatingTerminalCwdRequest,
   GitHubIssueUpdate,
+  GitHubReactionContent,
   GitHubPRRefreshCandidate,
   GitHubPRRefreshEnqueueResult,
   GitHubPRRefreshEvent,
@@ -1882,6 +1883,15 @@ export type PreloadApi = {
       prRepo?: GitHubOwnerRepo | null
       noCache?: boolean
     }) => Promise<PRComment[]>
+    setPRCommentReaction: (args: {
+      repoPath: string
+      repoId?: string
+      sourceContext?: TaskSourceContext | null
+      reactionSubjectId: string
+      content: GitHubReactionContent
+      reacted: boolean
+      prRepo?: GitHubOwnerRepo | null
+    }) => Promise<boolean>
     resolveReviewThread: (args: {
       repoPath: string
       repoId?: string
diff --git a/src/preload/index.ts b/src/preload/index.ts
index 8b192819496..2cf88323b23 100644
--- a/src/preload/index.ts
+++ b/src/preload/index.ts
@@ -75,6 +75,7 @@ import type {
   GitHubCommentResult,
   GitHubCreateIssueResult,
   GitHubOwnerRepo,
+  GitHubReactionContent,
   GitHubWorkItem,
   JiraProjectStatusOrder,
   GitPushTarget,
@@ -1470,6 +1471,16 @@ const api = {
       noCache?: boolean
     }): Promise<unknown[]> => ipcRenderer.invoke('gh:prComments', args),
 
+    setPRCommentReaction: (args: {
+      repoPath: string
+      repoId?: string
+      sourceContext?: TaskSourceContext | null
+      reactionSubjectId: string
+      content: GitHubReactionContent
+      reacted: boolean
+      prRepo?: GitHubOwnerRepo | null
+    }): Promise<boolean> => ipcRenderer.invoke('gh:setPRCommentReaction', args),
+
     resolveReviewThread: (args: {
       repoPath: string
       repoId?: string
diff --git a/src/renderer/src/components/github/CommentReactions.tsx b/src/renderer/src/components/github/CommentReactions.tsx
index 9c362b6520d..bbdca0fbe3d 100644
--- a/src/renderer/src/components/github/CommentReactions.tsx
+++ b/src/renderer/src/components/github/CommentReactions.tsx
@@ -1,6 +1,12 @@
 import React from 'react'
+import { SmilePlus } from 'lucide-react'
+import { Button } from '@/components/ui/button'
+import { Popover, PopoverContent, PopoverTrigger } from '@/components/ui/popover'
+import { Tooltip, TooltipContent, TooltipTrigger } from '@/components/ui/tooltip'
 import { translate } from '@/i18n/i18n'
-import type { GitHubReaction } from '../../../../shared/types'
+import { cn } from '@/lib/utils'
+import { GITHUB_REACTION_ORDER } from '@/lib/pr-comment-reactions'
+import type { GitHubReaction, GitHubReactionContent } from '../../../../shared/types'
 
 const REACTION_EMOJI: Record<GitHubReaction['content'], string> = {
   '+1': '👍',
@@ -13,36 +19,160 @@ const REACTION_EMOJI: Record<GitHubReaction['content'], string> = {
   eyes: '👀'
 }
 
+const REACTION_LABEL: Record<GitHubReactionContent, string> = {
+  '+1': 'thumbs up',
+  '-1': 'thumbs down',
+  laugh: 'laugh',
+  confused: 'confused',
+  heart: 'heart',
+  hooray: 'hooray',
+  rocket: 'rocket',
+  eyes: 'eyes'
+}
+
 export function CommentReactions({
-  reactions
+  reactions,
+  className,
+  onReactionChange
 }: {
   reactions?: GitHubReaction[]
+  className?: string
+  onReactionChange?: (content: GitHubReactionContent, reacted: boolean) => Promise<void> | void
 }): React.JSX.Element | null {
   const visibleReactions = (reactions ?? []).filter((reaction) => reaction.count > 0)
-  if (visibleReactions.length === 0) {
+  const [open, setOpen] = React.useState(false)
+  const [pendingContent, setPendingContent] = React.useState<GitHubReactionContent | null>(null)
+  if (visibleReactions.length === 0 && !onReactionChange) {
     return null
   }
 
+  const changeReaction = async (
+    content: GitHubReactionContent,
+    reacted: boolean
+  ): Promise<void> => {
+    if (!onReactionChange || pendingContent) {
+      return
+    }
+    setPendingContent(content)
+    setOpen(false)
+    try {
+      await onReactionChange(content, reacted)
+    } finally {
+      setPendingContent(null)
+    }
+  }
+
+  const pickerLabel = translate(
+    'auto.components.github.CommentReactions.addReaction',
+    'Add reaction'
+  )
+
   return (
-    <div className="mt-2 flex flex-wrap gap-1.5">
+    <div className={cn('mt-2 flex flex-wrap items-center gap-1.5', className)}>
       {visibleReactions.map((reaction) => (
-        <span
-          key={reaction.content}
-          className="inline-flex h-6 items-center gap-1 rounded-full border border-border/60 bg-muted/35 px-2 text-[12px] leading-none text-foreground"
-          aria-label={translate(
-            'auto.components.GitHubItemDialog.a18f669c7a',
-            '{{value0}} {{value1}} reaction{{value2}}',
-            {
-              value0: reaction.count,
-              value1: reaction.content,
-              value2: reaction.count === 1 ? '' : 's'
-            }
+        <React.Fragment key={reaction.content}>
+          {onReactionChange ? (
+            <Button
+              type="button"
+              variant="outline"
+              size="xs"
+              disabled={pendingContent !== null}
+              className={cn(
+                'h-6 gap-1 rounded-full px-2 text-[12px] font-normal',
+                reaction.viewerHasReacted && 'border-ring bg-accent text-accent-foreground'
+              )}
+              aria-pressed={Boolean(reaction.viewerHasReacted)}
+              aria-label={translate(
+                'auto.components.GitHubItemDialog.a18f669c7a',
+                '{{value0}} {{value1}} reaction{{value2}}',
+                {
+                  value0: reaction.count,
+                  value1: REACTION_LABEL[reaction.content],
+                  value2: reaction.count === 1 ? '' : 's'
+                }
+              )}
+              onClick={() => void changeReaction(reaction.content, !reaction.viewerHasReacted)}
+            >
+              <span aria-hidden="true">{REACTION_EMOJI[reaction.content]}</span>
+              <span className="tabular-nums">{reaction.count}</span>
+            </Button>
+          ) : (
+            <span
+              className="inline-flex h-6 items-center gap-1 rounded-full border border-border/60 bg-muted/35 px-2 text-[12px] leading-none text-foreground"
+              aria-label={translate(
+                'auto.components.GitHubItemDialog.a18f669c7a',
+                '{{value0}} {{value1}} reaction{{value2}}',
+                {
+                  value0: reaction.count,
+                  value1: REACTION_LABEL[reaction.content],
+                  value2: reaction.count === 1 ? '' : 's'
+                }
+              )}
+            >
+              <span aria-hidden="true">{REACTION_EMOJI[reaction.content]}</span>
+              <span className="tabular-nums">{reaction.count}</span>
+            </span>
           )}
-        >
-          <span aria-hidden="true">{REACTION_EMOJI[reaction.content]}</span>
-          <span className="tabular-nums">{reaction.count}</span>
-        </span>
+        </React.Fragment>
       ))}
+      {onReactionChange ? (
+        <Popover open={open} onOpenChange={(nextOpen) => !pendingContent && setOpen(nextOpen)}>
+          <Tooltip>
+            <TooltipTrigger asChild>
+              <PopoverTrigger asChild>
+                <Button
+                  type="button"
+                  variant="ghost"
+                  size="icon-xs"
+                  disabled={pendingContent !== null}
+                  className="text-muted-foreground hover:text-foreground"
+                  aria-label={pickerLabel}
+                >
+                  <SmilePlus className="size-3.5" />
+                </Button>
+              </PopoverTrigger>
+            </TooltipTrigger>
+            <TooltipContent side="top" sideOffset={4}>
+              {pickerLabel}
+            </TooltipContent>
+          </Tooltip>
+          <PopoverContent align="start" side="top" sideOffset={6} className="w-auto p-1.5">
+            <div className="grid grid-cols-4 gap-1" aria-label={pickerLabel} role="group">
+              {GITHUB_REACTION_ORDER.map((content) => {
+                const reaction = reactions?.find((candidate) => candidate.content === content)
+                const reacted = Boolean(reaction?.viewerHasReacted)
+                return (
+                  <Button
+                    key={content}
+                    type="button"
+                    variant="ghost"
+                    size="icon-sm"
+                    disabled={pendingContent !== null}
+                    className={cn('text-lg', reacted && 'bg-accent text-accent-foreground')}
+                    aria-label={
+                      reacted
+                        ? translate(
+                            'auto.components.github.CommentReactions.removeNamedReaction',
+                            'Remove {{value0}} reaction',
+                            { value0: REACTION_LABEL[content] }
+                          )
+                        : translate(
+                            'auto.components.github.CommentReactions.addNamedReaction',
+                            'Add {{value0}} reaction',
+                            { value0: REACTION_LABEL[content] }
+                          )
+                    }
+                    aria-pressed={reacted}
+                    onClick={() => void changeReaction(content, !reacted)}
+                  >
+                    <span aria-hidden="true">{REACTION_EMOJI[content]}</span>
+                  </Button>
+                )
+              })}
+            </div>
+          </PopoverContent>
+        </Popover>
+      ) : null}
     </div>
   )
 }
diff --git a/src/renderer/src/components/right-sidebar/ChecksPanel.tsx b/src/renderer/src/components/right-sidebar/ChecksPanel.tsx
index 028abac821c..44abe773e62 100644
--- a/src/renderer/src/components/right-sidebar/ChecksPanel.tsx
+++ b/src/renderer/src/components/right-sidebar/ChecksPanel.tsx
@@ -25,6 +25,7 @@ import { useActiveWorktree, useRepoById } from '@/store/selectors'
 import { useChecksPanelTerminalWorktree } from './use-checks-panel-terminal-worktree'
 import { cn } from '@/lib/utils'
 import { openHttpLink } from '@/lib/http-link-routing'
+import { setReactionOnSubject } from '@/lib/pr-comment-reactions'
 import { Button } from '@/components/ui/button'
 import { DetachedHeadBadge } from '@/components/DetachedHeadBadge'
 import {
@@ -64,6 +65,7 @@ import type {
   PRCheckDetail,
   PRCheckRunDetails,
   PRComment,
+  GitHubReactionContent,
   PRRefreshErrorType
 } from '../../../../shared/types'
 import { getConnectionId } from '@/lib/connection-context'
@@ -496,6 +498,7 @@ export default function ChecksPanel(): React.JSX.Element {
   const fetchPRComments = useAppStore((s) => s.fetchPRComments)
   const addPRConversationComment = useAppStore((s) => s.addPRConversationComment)
   const addPRReviewCommentReply = useAppStore((s) => s.addPRReviewCommentReply)
+  const setPRCommentReaction = useAppStore((s) => s.setPRCommentReaction)
   const resolveReviewThread = useAppStore((s) => s.resolveReviewThread)
   const detectedAgentIds = useAppStore((s) => s.detectedAgentIds)
   const remoteDetectedAgentIds = useAppStore((s) => {
@@ -2941,6 +2944,49 @@ export default function ChecksPanel(): React.JSX.Element {
     [pr?.prRepo, confirm]
   )
 
+  const handleSetReaction = useCallback(
+    async (comment: PRComment, content: GitHubReactionContent, reacted: boolean): Promise<void> => {
+      const reactionSubjectId = comment.reactionSubjectId
+      if (!repo || !prNumber || !pr?.prRepo || !reactionSubjectId) {
+        return
+      }
+      const requestKey = checksPanelAsyncResultKey(
+        prCacheKey,
+        branch,
+        prNumber,
+        pr.prRepo,
+        pr.headSha
+      )
+      const previousReactions = comment.reactions
+      setComments((current) => setReactionOnSubject(current, reactionSubjectId, content, reacted))
+      const ok = await setPRCommentReaction(
+        repo.path,
+        prNumber,
+        reactionSubjectId,
+        content,
+        reacted,
+        { repoId: repo.id, prRepo: pr.prRepo }
+      )
+      if (!isCurrentAsyncResult(requestKey) || ok) {
+        return
+      }
+      setComments((current) =>
+        current.map((entry) =>
+          entry.reactionSubjectId === reactionSubjectId
+            ? { ...entry, reactions: previousReactions }
+            : entry
+        )
+      )
+      toast.error(
+        translate(
+          'auto.components.right.sidebar.ChecksPanel.updateReactionFailed',
+          'Failed to update reaction.'
+        )
+      )
+    },
+    [branch, isCurrentAsyncResult, pr, prCacheKey, prNumber, repo, setPRCommentReaction]
+  )
+
   const handleReplyToComment = useCallback(
     async (comment: PRComment, body: string, options: { notifyOnFailure?: boolean } = {}) => {
       const notifyOnFailure = options.notifyOnFailure !== false
@@ -4506,6 +4552,7 @@ export default function ChecksPanel(): React.JSX.Element {
         onResolve={pr || activeGitLabReview ? handleResolve : undefined}
         onEditComment={pr ? handleEditComment : undefined}
         onDeleteComment={pr ? handleDeleteComment : undefined}
+        onSetReaction={canTargetPRComments ? handleSetReaction : undefined}
       />
       <SourceControlAgentActionDialog
         open={sourceControlAiActionsVisible && agentComposerState !== null}
diff --git a/src/renderer/src/components/right-sidebar/checks-panel-content.tsx b/src/renderer/src/components/right-sidebar/checks-panel-content.tsx
index 2b51b03f7b2..dda1c3ee4e1 100644
--- a/src/renderer/src/components/right-sidebar/checks-panel-content.tsx
+++ b/src/renderer/src/components/right-sidebar/checks-panel-content.tsx
@@ -55,6 +55,7 @@ import {
 } from '@/components/ui/context-menu'
 import { cn } from '@/lib/utils'
 import CommentMarkdown from '@/components/sidebar/CommentMarkdown'
+import { CommentReactions } from '@/components/github/CommentReactions'
 import { CheckJobLogTail } from './check-job-log-tail'
 import {
   filterPRCommentsByAudience,
@@ -86,6 +87,7 @@ import type {
   PRCheckDetail,
   PRCheckRunDetails,
   PRComment,
+  GitHubReactionContent,
   PRConflictSummary,
   PRMergeableState
 } from '../../../../shared/types'
@@ -1732,6 +1734,7 @@ function CommentRow({
   onReply,
   onEditComment,
   onDeleteComment,
+  onSetReaction,
   onQueueForAgent
 }: {
   comment: PRComment
@@ -1749,6 +1752,11 @@ function CommentRow({
   onReply?: (comment: PRComment) => void
   onEditComment?: (comment: PRComment, body: string) => Promise<boolean>
   onDeleteComment?: (comment: PRComment) => void | Promise<void>
+  onSetReaction?: (
+    comment: PRComment,
+    content: GitHubReactionContent,
+    reacted: boolean
+  ) => Promise<void>
   onQueueForAgent?: () => void
 }): React.JSX.Element {
   const automated = isBotPRComment(comment, botAuthorOverrides)
@@ -2007,13 +2015,17 @@ function CommentRow({
             </div>
           </div>
         ) : (
-          <CommentMarkdown
-            content={comment.body}
-            className={cn(
-              isReply ? presentation.commentBodyReply : presentation.commentBody,
-              presentation.commentBodyMarkdown
-            )}
-          />
+          <div className={isReply ? presentation.commentBodyReply : presentation.commentBody}>
+            <CommentMarkdown content={comment.body} className={presentation.commentBodyMarkdown} />
+            <CommentReactions
+              reactions={comment.reactions}
+              onReactionChange={
+                comment.reactionSubjectId && onSetReaction
+                  ? (content, reacted) => onSetReaction(comment, content, reacted)
+                  : undefined
+              }
+            />
+          </div>
         )}
       </div>
     </div>
@@ -2036,6 +2048,7 @@ function PRCommentGroupView({
   onReply,
   onEditComment,
   onDeleteComment,
+  onSetReaction,
   onQueueForAgent
 }: {
   group: PRCommentGroup
@@ -2053,6 +2066,11 @@ function PRCommentGroupView({
   onReply?: (comment: PRComment, body: string) => Promise<RightPanelCommentSubmitResult>
   onEditComment?: (comment: PRComment, body: string) => Promise<boolean>
   onDeleteComment?: (comment: PRComment) => void | Promise<void>
+  onSetReaction?: (
+    comment: PRComment,
+    content: GitHubReactionContent,
+    reacted: boolean
+  ) => Promise<void>
   onQueueForAgent?: () => void
 }): React.JSX.Element {
   // Reply targets a specific comment id so any comment in a thread — root or
@@ -2099,6 +2117,7 @@ function PRCommentGroupView({
     onResolve,
     onEditComment,
     onDeleteComment,
+    onSetReaction,
     onQueueForAgent
   }
 
@@ -2181,7 +2200,8 @@ function ResolvedCommentGroupsSection({
   onCancelReply,
   onReply,
   onEditComment,
-  onDeleteComment
+  onDeleteComment,
+  onSetReaction
 }: {
   groups: PRCommentGroup[]
   botAuthorOverrides: ReadonlySet<string>
@@ -2195,6 +2215,11 @@ function ResolvedCommentGroupsSection({
   onReply?: (comment: PRComment, body: string) => Promise<RightPanelCommentSubmitResult>
   onEditComment?: (comment: PRComment, body: string) => Promise<boolean>
   onDeleteComment?: (comment: PRComment) => void | Promise<void>
+  onSetReaction?: (
+    comment: PRComment,
+    content: GitHubReactionContent,
+    reacted: boolean
+  ) => Promise<void>
 }): React.JSX.Element | null {
   if (groups.length === 0) {
     return null
@@ -2230,6 +2255,7 @@ function ResolvedCommentGroupsSection({
                 onReply={onReply}
                 onEditComment={onEditComment}
                 onDeleteComment={onDeleteComment}
+                onSetReaction={onSetReaction}
               />
             ))}
           </AccordionContent>
@@ -2296,7 +2322,8 @@ export function PRCommentsList({
   onReply,
   onResolve,
   onEditComment,
-  onDeleteComment
+  onDeleteComment,
+  onSetReaction
 }: {
   comments: PRComment[]
   commentsLoading: boolean
@@ -2313,6 +2340,11 @@ export function PRCommentsList({
   onResolve?: (threadId: string, resolve: boolean) => boolean | Promise<boolean>
   onEditComment?: (comment: PRComment, body: string) => Promise<boolean>
   onDeleteComment?: (comment: PRComment) => void | Promise<void>
+  onSetReaction?: (
+    comment: PRComment,
+    content: GitHubReactionContent,
+    reacted: boolean
+  ) => Promise<void>
 }): React.JSX.Element {
   const presentation = React.useMemo(() => getPRCommentPresentationClasses(), [])
   const [commentFilter, setCommentFilter] = useState<PRCommentAudienceFilter>('all')
@@ -2435,6 +2467,7 @@ export function PRCommentsList({
         onReply={onReply}
         onEditComment={onEditComment}
         onDeleteComment={onDeleteComment}
+        onSetReaction={onSetReaction}
         onQueueForAgent={canQueue ? () => addGroupToSelection(groupId) : undefined}
       />
     )
@@ -2765,6 +2798,7 @@ export function PRCommentsList({
                 onReply={onReply}
                 onEditComment={onEditComment}
                 onDeleteComment={onDeleteComment}
+                onSetReaction={onSetReaction}
               />
             </>
           )}
diff --git a/src/renderer/src/i18n/locales/en.json b/src/renderer/src/i18n/locales/en.json
index 3184344d835..baadf663b56 100644
--- a/src/renderer/src/i18n/locales/en.json
+++ b/src/renderer/src/i18n/locales/en.json
@@ -2412,6 +2412,11 @@
             "label": "Close as duplicate",
             "description": "Duplicate of another issue"
           }
+        },
+        "CommentReactions": {
+          "addReaction": "Add reaction",
+          "removeNamedReaction": "Remove {{value0}} reaction",
+          "addNamedReaction": "Add {{value0}} reaction"
         }
       },
       "linear": {
@@ -10566,7 +10571,8 @@
               "pending": "Syncing…",
               "branch": "Sync Branch"
             },
-            "7e4b2a19c0": "Could not resolve the GitHub PR to reply on."
+            "7e4b2a19c0": "Could not resolve the GitHub PR to reply on.",
+            "updateReactionFailed": "Failed to update reaction."
           },
           "CreatePullRequestDialog": {
             "2bc1b4345e": "Cancel",
diff --git a/src/renderer/src/lib/pr-comment-reactions.test.ts b/src/renderer/src/lib/pr-comment-reactions.test.ts
new file mode 100644
index 00000000000..5e5b69fab20
--- /dev/null
+++ b/src/renderer/src/lib/pr-comment-reactions.test.ts
@@ -0,0 +1,49 @@
+import { describe, expect, it } from 'vitest'
+import type { PRComment } from '../../../shared/types'
+import { setCommentReaction, setReactionOnSubject } from './pr-comment-reactions'
+
+function comment(overrides: Partial<PRComment> = {}): PRComment {
+  return {
+    id: 1,
+    author: 'octocat',
+    authorAvatarUrl: '',
+    body: 'Looks good',
+    createdAt: '2026-08-09T12:00:00Z',
+    url: 'https://github.com/acme/orca/pull/1#issuecomment-1',
+    ...overrides
+  }
+}
+
+describe('setCommentReaction', () => {
+  it('adds a viewer reaction in GitHub order', () => {
+    expect(
+      setCommentReaction(
+        comment({ reactions: [{ content: 'heart', count: 2, viewerHasReacted: false }] }),
+        '+1',
+        true
+      ).reactions
+    ).toEqual([
+      { content: '+1', count: 1, viewerHasReacted: true },
+      { content: 'heart', count: 2, viewerHasReacted: false }
+    ])
+  })
+
+  it('removes the final viewer reaction', () => {
+    expect(
+      setCommentReaction(
+        comment({ reactions: [{ content: 'rocket', count: 1, viewerHasReacted: true }] }),
+        'rocket',
+        false
+      ).reactions
+    ).toBeUndefined()
+  })
+
+  it('updates only the targeted comment', () => {
+    const target = comment({ reactionSubjectId: 'IC_1' })
+    const other = comment({ id: 2, reactionSubjectId: 'IC_2' })
+    const result = setReactionOnSubject([target, other], 'IC_1', 'eyes', true)
+
+    expect(result[0].reactions).toEqual([{ content: 'eyes', count: 1, viewerHasReacted: true }])
+    expect(result[1]).toBe(other)
+  })
+})
diff --git a/src/renderer/src/lib/pr-comment-reactions.ts b/src/renderer/src/lib/pr-comment-reactions.ts
new file mode 100644
index 00000000000..80f67303456
--- /dev/null
+++ b/src/renderer/src/lib/pr-comment-reactions.ts
@@ -0,0 +1,53 @@
+import type { GitHubReaction, GitHubReactionContent, PRComment } from '../../../shared/types'
+
+export const GITHUB_REACTION_ORDER: readonly GitHubReactionContent[] = [
+  '+1',
+  '-1',
+  'laugh',
+  'confused',
+  'heart',
+  'hooray',
+  'rocket',
+  'eyes'
+]
+
+export function setCommentReaction(
+  comment: PRComment,
+  content: GitHubReactionContent,
+  reacted: boolean
+): PRComment {
+  const reactions = comment.reactions ?? []
+  const current = reactions.find((reaction) => reaction.content === content)
+  if (Boolean(current?.viewerHasReacted) === reacted) {
+    return comment
+  }
+
+  const nextCount = Math.max(0, (current?.count ?? 0) + (reacted ? 1 : -1))
+  const nextReaction: GitHubReaction = {
+    content,
+    count: nextCount,
+    viewerHasReacted: reacted
+  }
+  const nextReactions = reactions
+    .filter((reaction) => reaction.content !== content)
+    .concat(nextCount > 0 ? nextReaction : [])
+    .sort(
+      (left, right) =>
+        GITHUB_REACTION_ORDER.indexOf(left.content) - GITHUB_REACTION_ORDER.indexOf(right.content)
+    )
+
+  return { ...comment, reactions: nextReactions.length > 0 ? nextReactions : undefined }
+}
+
+export function setReactionOnSubject(
+  comments: readonly PRComment[],
+  reactionSubjectId: string,
+  content: GitHubReactionContent,
+  reacted: boolean
+): PRComment[] {
+  return comments.map((comment) =>
+    comment.reactionSubjectId === reactionSubjectId
+      ? setCommentReaction(comment, content, reacted)
+      : comment
+  )
+}
diff --git a/src/renderer/src/store/slices/github.test.ts b/src/renderer/src/store/slices/github.test.ts
index c3947d58c28..05866e6ec71 100644
--- a/src/renderer/src/store/slices/github.test.ts
+++ b/src/renderer/src/store/slices/github.test.ts
@@ -45,6 +45,7 @@ const mockApi = {
     prComments: vi.fn().mockResolvedValue([]),
     addIssueComment: vi.fn(),
     addPRReviewCommentReply: vi.fn(),
+    setPRCommentReaction: vi.fn(),
     resolveReviewThread: vi.fn(),
     listWorkItems: vi.fn(),
     countWorkItems: vi.fn().mockResolvedValue(0),
@@ -1503,6 +1504,7 @@ describe('createGitHubSlice PR comment mutations', () => {
         url: ''
       }
     })
+    mockApi.gh.setPRCommentReaction.mockResolvedValue(true)
   })
 
   it('deduplicates merged PR comments and preserves existing thread metadata', () => {
@@ -1666,6 +1668,131 @@ describe('createGitHubSlice PR comment mutations', () => {
     ).toMatchObject({ body: 'reply', threadId: 'PRRT_1', path: 'src/a.ts', line: 8 })
   })
 
+  it('updates cached reactions through local GitHub IPC', async () => {
+    const store = createTestStore()
+    const repoPath = '/repo'
+    const repoId = 'repo-id'
+    const cacheKey = `${repoId}::pr-comments::acme/widgets::12`
+    store.setState({
+      repos: [{ id: repoId, path: repoPath, name: 'repo', kind: 'git' }],
+      commentsCache: {
+        [cacheKey]: {
+          data: [
+            {
+              id: 10,
+              reactionSubjectId: 'IC_10',
+              author: 'reviewer',
+              authorAvatarUrl: '',
+              body: 'Nice',
+              createdAt: '2026-03-28T00:00:00Z',
+              url: ''
+            }
+          ],
+          fetchedAt: 1
+        }
+      }
+    } as unknown as Partial<AppState>)
+
+    await store.getState().setPRCommentReaction(repoPath, 12, 'IC_10', 'heart', true, {
+      repoId,
+      prRepo: { owner: 'Acme', repo: 'Widgets' }
+    })
+
+    expect(mockApi.gh.setPRCommentReaction).toHaveBeenCalledWith({
+      repoPath,
+      repoId,
+      reactionSubjectId: 'IC_10',
+      content: 'heart',
+      reacted: true,
+      prRepo: { owner: 'Acme', repo: 'Widgets' },
+      sourceContext: undefined
+    })
+    expect(store.getState().commentsCache[cacheKey]?.data?.[0].reactions).toEqual([
+      { content: 'heart', count: 1, viewerHasReacted: true }
+    ])
+  })
+
+  it('rolls back an optimistic reaction when GitHub rejects it', async () => {
+    mockApi.gh.setPRCommentReaction.mockResolvedValueOnce(false)
+    const store = createTestStore()
+    const repoPath = '/repo'
+    const repoId = 'repo-id'
+    const cacheKey = `${repoId}::pr-comments::acme/widgets::12`
+    store.setState({
+      repos: [{ id: repoId, path: repoPath, name: 'repo', kind: 'git' }],
+      commentsCache: {
+        [cacheKey]: {
+          data: [
+            {
+              id: 10,
+              reactionSubjectId: 'IC_10',
+              author: 'reviewer',
+              authorAvatarUrl: '',
+              body: 'Nice',
+              createdAt: '2026-03-28T00:00:00Z',
+              url: '',
+              reactions: [{ content: 'heart', count: 2, viewerHasReacted: false }]
+            }
+          ],
+          fetchedAt: 1
+        }
+      }
+    } as unknown as Partial<AppState>)
+
+    const ok = await store.getState().setPRCommentReaction(repoPath, 12, 'IC_10', 'heart', true, {
+      repoId,
+      prRepo: { owner: 'Acme', repo: 'Widgets' }
+    })
+
+    expect(ok).toBe(false)
+    expect(store.getState().commentsCache[cacheKey]?.data?.[0].reactions).toEqual([
+      { content: 'heart', count: 2, viewerHasReacted: false }
+    ])
+  })
+
+  it('routes reaction mutations through the workspace runtime', async () => {
+    runtimeEnvironmentCall.mockResolvedValueOnce({
+      id: 'rpc-pr-reaction',
+      ok: true,
+      result: true,
+      _meta: { runtimeId: 'remote-runtime' }
+    })
+    const store = createTestStore()
+    const repoPath = '/repo'
+    const repoId = 'repo-id'
+    store.setState({
+      settings: { activeRuntimeEnvironmentId: 'env-1' } as AppState['settings'],
+      repos: [
+        {
+          id: repoId,
+          path: repoPath,
+          name: 'repo',
+          kind: 'git',
+          executionHostId: 'runtime:env-1'
+        }
+      ]
+    } as unknown as Partial<AppState>)
+
+    await store.getState().setPRCommentReaction(repoPath, 12, 'PRRC_10', 'rocket', true, {
+      repoId,
+      prRepo: { owner: 'Acme', repo: 'Widgets' }
+    })
+
+    expect(runtimeEnvironmentCall).toHaveBeenCalledWith({
+      selector: 'env-1',
+      method: 'github.setPRCommentReaction',
+      params: {
+        repo: repoId,
+        reactionSubjectId: 'PRRC_10',
+        content: 'rocket',
+        reacted: true,
+        prRepo: { owner: 'Acme', repo: 'Widgets' }
+      },
+      timeoutMs: 30_000
+    })
+    expect(mockApi.gh.setPRCommentReaction).not.toHaveBeenCalled()
+  })
+
   it('does not mutate the PR comments cache when GitHub omits the comment payload', async () => {
     mockApi.gh.addIssueComment.mockResolvedValueOnce({ ok: true })
     const store = createTestStore()
diff --git a/src/renderer/src/store/slices/github.ts b/src/renderer/src/store/slices/github.ts
index 599ef6cd960..d1d0ebe886c 100644
--- a/src/renderer/src/store/slices/github.ts
+++ b/src/renderer/src/store/slices/github.ts
@@ -17,6 +17,7 @@ import type {
   PRRefreshErrorType,
   PRRefreshOutcome,
   GitHubCommentResult,
+  GitHubReactionContent,
   IssueInfo,
   PRCheckDetail,
   PRCheckRunDetails,
@@ -74,6 +75,7 @@ import {
   type TaskSourceContext
 } from '../../../../shared/task-source-context'
 import { normalizeGitHubPRForBranchOutcome } from '../../../../shared/github-pr-for-branch-outcome'
+import { setReactionOnSubject } from '@/lib/pr-comment-reactions'
 
 // ─── ProjectV2 cache types ────────────────────────────────────────────
 // Why: separate from CacheEntry<T> — project-view has a single GraphQL source (no issue/PR fallback) and a distinct error union.
@@ -1890,6 +1892,14 @@ export type GitHubSlice = {
       line?: number
     }
   ) => Promise<GitHubCommentResult>
+  setPRCommentReaction: (
+    repoPath: string,
+    prNumber: number,
+    reactionSubjectId: string,
+    content: GitHubReactionContent,
+    reacted: boolean,
+    options?: RepoScopedFetchOptions & { prRepo?: GitHubOwnerRepo | null }
+  ) => Promise<boolean>
   resolveReviewThread: (
     repoPath: string,
     prNumber: number,
@@ -3839,6 +3849,111 @@ export const createGitHubSlice: StateCreator<AppState, [], [], GitHubSlice> = (s
     return { ok: true, comment }
   },
 
+  setPRCommentReaction: async (
+    repoPath,
+    prNumber,
+    reactionSubjectId,
+    content,
+    reacted,
+    options
+  ) => {
+    const repo = get().repos?.find((candidate) =>
+      options?.repoId ? candidate.id === options.repoId : candidate.path === repoPath
+    )
+    const repoId = options?.repoId ?? repo?.id
+    const requestSettings = getGitHubRepoSourceSettings(
+      get().settings,
+      repo,
+      options?.sourceContext
+    )
+    const cacheKey = sourceScopedRepoCacheKey(
+      repoPath,
+      repoId,
+      prCommentsCacheSuffix(prNumber, options?.prRepo),
+      requestSettings,
+      repo?.connectionId,
+      repo?.executionHostId,
+      options?.sourceContext,
+      repo !== undefined
+    )
+    const previousComment = get().commentsCache[cacheKey]?.data?.find(
+      (comment) => comment.reactionSubjectId === reactionSubjectId
+    )
+    set((state) => {
+      const entry = state.commentsCache[cacheKey]
+      if (!entry?.data) {
+        return state
+      }
+      return {
+        commentsCache: {
+          ...state.commentsCache,
+          [cacheKey]: {
+            ...entry,
+            data: setReactionOnSubject(entry.data, reactionSubjectId, content, reacted)
+          }
+        }
+      }
+    })
+
+    const requestContext = getGitHubWorkItemRequestContext(
+      get(),
+      requestSettings,
+      repoId ?? repoPath,
+      repoPath,
+      options?.sourceContext
+    )
+    let ok = false
+    try {
+      ok =
+        requestContext.target.kind === 'environment'
+          ? await callRuntimeRpc<boolean>(
+              { kind: 'environment', environmentId: requestContext.target.environmentId },
+              'github.setPRCommentReaction',
+              {
+                repo: requestContext.target.runtimeRepoId,
+                reactionSubjectId,
+                content,
+                reacted,
+                prRepo: options?.prRepo ?? null
+              },
+              { timeoutMs: 30_000 }
+            )
+          : await window.api.gh.setPRCommentReaction({
+              repoPath,
+              repoId,
+              reactionSubjectId,
+              content,
+              reacted,
+              prRepo: options?.prRepo ?? null,
+              sourceContext: options?.sourceContext
+            })
+    } catch (err) {
+      console.error('Failed to update PR comment reaction:', err)
+    }
+    if (!ok && previousComment) {
+      set((state) => {
+        const entry = state.commentsCache[cacheKey]
+        if (!entry?.data) {
+          return state
+        }
+        return {
+          commentsCache: {
+            ...state.commentsCache,
+            [cacheKey]: {
+              ...entry,
+              data: entry.data.map((comment) =>
+                comment.reactionSubjectId === reactionSubjectId
+                  ? { ...comment, reactions: previousComment.reactions }
+                  : comment
+              )
+            }
+          }
+        }
+      })
+    }
+    return ok
+  },
+
   resolveReviewThread: async (repoPath, prNumber, threadId, resolve, options) => {
     const repo = get().repos?.find((candidate) =>
       options?.repoId ? candidate.id === options.repoId : candidate.path === repoPath
diff --git a/src/renderer/src/web/web-preload-api.test.ts b/src/renderer/src/web/web-preload-api.test.ts
index 92dd209d047..cc508040e49 100644
--- a/src/renderer/src/web/web-preload-api.test.ts
+++ b/src/renderer/src/web/web-preload-api.test.ts
@@ -3769,6 +3769,7 @@ describe('web GitHub preload API', () => {
         'resolveProjectRef',
         'resolveReviewThread',
         'setPRAutoMerge',
+        'setPRCommentReaction',
         'setPRFileViewed',
         'starOrca',
         'updateIssue',
@@ -3950,6 +3951,17 @@ describe('web GitHub preload API', () => {
         expectedMethod: 'github.prComments',
         expectedParams: withRepo({ repoPath, prNumber: 7, noCache: true })
       },
+      {
+        key: 'setPRCommentReaction',
+        args: { repoPath, reactionSubjectId: 'IC_1', content: 'heart', reacted: true },
+        expectedMethod: 'github.setPRCommentReaction',
+        expectedParams: withRepo({
+          repoPath,
+          reactionSubjectId: 'IC_1',
+          content: 'heart',
+          reacted: true
+        })
+      },
       {
         key: 'resolveReviewThread',
         args: { repoPath, threadId: 'thread-1', resolve: true },
diff --git a/src/renderer/src/web/web-preload-api.ts b/src/renderer/src/web/web-preload-api.ts
index 6f049d237c8..038e05e1373 100644
--- a/src/renderer/src/web/web-preload-api.ts
+++ b/src/renderer/src/web/web-preload-api.ts
@@ -289,6 +289,7 @@ type WebGitHubRouteKey =
   | 'prCheckDetails'
   | 'rerunPRChecks'
   | 'prComments'
+  | 'setPRCommentReaction'
   | 'resolveReviewThread'
   | 'setPRFileViewed'
   | 'updatePRTitle'
@@ -337,6 +338,7 @@ type WebGitHubRuntimeMethod =
   | 'github.prCheckDetails'
   | 'github.rerunPRChecks'
   | 'github.prComments'
+  | 'github.setPRCommentReaction'
   | 'github.resolveReviewThread'
   | 'github.setPRFileViewed'
   | 'github.updatePRTitle'
@@ -438,6 +440,7 @@ export const GITHUB_WEB_RPC_METHODS = {
   prCheckDetails: 'github.prCheckDetails',
   rerunPRChecks: 'github.rerunPRChecks',
   prComments: 'github.prComments',
+  setPRCommentReaction: 'github.setPRCommentReaction',
   resolveReviewThread: 'github.resolveReviewThread',
   setPRFileViewed: 'github.setPRFileViewed',
   updatePRTitle: 'github.updatePRTitle',
@@ -2385,6 +2388,11 @@ function createGitHubApi(): WebGitHubApi {
       route<WebGitHubResult<'rerunPRChecks'>>(GITHUB_WEB_RPC_METHODS.rerunPRChecks, args),
     prComments: (args) =>
       route<WebGitHubResult<'prComments'>>(GITHUB_WEB_RPC_METHODS.prComments, args),
+    setPRCommentReaction: (args) =>
+      route<WebGitHubResult<'setPRCommentReaction'>>(
+        GITHUB_WEB_RPC_METHODS.setPRCommentReaction,
+        args
+      ),
     resolveReviewThread: (args) =>
       route<WebGitHubResult<'resolveReviewThread'>>(
         GITHUB_WEB_RPC_METHODS.resolveReviewThread,
diff --git a/src/shared/types.ts b/src/shared/types.ts
index c6dfff01d3c..9eb3de46c3b 100644
--- a/src/shared/types.ts
+++ b/src/shared/types.ts
@@ -1485,6 +1485,7 @@ export type GitHubReactionContent =
 export type GitHubReaction = {
   content: GitHubReactionContent
   count: number
+  viewerHasReacted?: boolean
 }
 
 export type PRComment = {
@@ -1495,6 +1496,8 @@ export type PRComment = {
   createdAt: string
   url: string
   reactions?: GitHubReaction[]
+  /** GraphQL node ID for GitHub comments that support reaction mutations. */
+  reactionSubjectId?: string
   /** File path for inline review comments (absent for top-level conversation comments). */
   path?: string
   /** GraphQL node ID of the review thread — present only for inline review comments.
diff --git a/tests/e2e/helpers/pr-comments-sidebar-fixture.ts b/tests/e2e/helpers/pr-comments-sidebar-fixture.ts
index c6784a2f282..b44aaa84c3c 100644
--- a/tests/e2e/helpers/pr-comments-sidebar-fixture.ts
+++ b/tests/e2e/helpers/pr-comments-sidebar-fixture.ts
@@ -15,6 +15,7 @@ export const FIXTURE_COMMENTS: PRComment[] = [
     body: 'Please update this handler before merge.',
     createdAt: '2026-05-14T10:00:00.000Z',
     url: 'https://github.com/acme/orca/pull/73#discussion_r101',
+    reactionSubjectId: 'PRRC_101',
     threadId: 'thread-open',
     path: 'src/handler.ts',
     isResolved: false
@@ -25,7 +26,8 @@ export const FIXTURE_COMMENTS: PRComment[] = [
     authorAvatarUrl: '',
     body: 'LGTM on the overall approach.',
     createdAt: '2026-05-14T11:00:00.000Z',
-    url: 'https://github.com/acme/orca/pull/73#issuecomment-102'
+    url: 'https://github.com/acme/orca/pull/73#issuecomment-102',
+    reactionSubjectId: 'IC_102'
   },
   {
     id: 103,
@@ -72,7 +74,8 @@ export async function seedPRCommentsSidebarFixture(page: Page): Promise<PRCommen
       url: `https://github.com/acme/orca/pull/${prNumber}`,
       checksStatus: 'pending',
       updatedAt: '2026-05-15T00:00:00.000Z',
-      mergeable: 'MERGEABLE'
+      mergeable: 'MERGEABLE',
+      prRepo: { owner: 'acme', repo: 'orca' }
     }
     const prCacheEntries = {
       [`${repo.id}::${branch}`]: {
@@ -131,6 +134,7 @@ export async function seedPRCommentsSidebarFixture(page: Page): Promise<PRCommen
       },
       fetchPRChecks: async () => [],
       fetchPRComments: async () => comments,
+      setPRCommentReaction: async () => true,
       fetchUpstreamStatus: async () => undefined,
       setUpstreamStatus: () => undefined
     }))
diff --git a/tests/e2e/pr-comments-sidebar-cards.spec.ts b/tests/e2e/pr-comments-sidebar-cards.spec.ts
index 9cccce81bfb..ee95b3f74cb 100644
--- a/tests/e2e/pr-comments-sidebar-cards.spec.ts
+++ b/tests/e2e/pr-comments-sidebar-cards.spec.ts
@@ -124,6 +124,39 @@ test.describe('PR comments sidebar cards view', () => {
     expect(positions[1]).toBeLessThan(positions[2])
   })
 
+  test('adds reactions to conversation and review-thread comments', async ({ orcaPage }) => {
+    const { worktreeId } = await seedPRCommentsSidebarFixture(orcaPage)
+    await openChecks(orcaPage, worktreeId)
+    await expect(orcaPage.getByText('Needs review · 1')).toBeVisible({ timeout: 10_000 })
+
+    const conversationCard = orcaPage.getByTestId('pr-comment-group').filter({
+      hasText: 'LGTM on the overall approach.'
+    })
+    const conversationReactionButton = conversationCard.getByRole('button', {
+      name: 'Add reaction'
+    })
+    await conversationReactionButton.evaluate((element) => (element as HTMLElement).click())
+    const heartReactionButton = orcaPage.getByRole('button', { name: 'Add heart reaction' })
+    await expect(heartReactionButton).toBeVisible()
+    await heartReactionButton.evaluate((element) => (element as HTMLElement).click())
+    await expect(
+      conversationCard.getByRole('button', { name: '1 heart reaction' })
+    ).toHaveAttribute('aria-pressed', 'true')
+    await expect(orcaPage.getByRole('button', { name: 'Add rocket reaction' })).toHaveCount(0)
+
+    const reviewThreadCard = orcaPage.getByTestId('pr-comment-group').filter({
+      hasText: 'Please update this handler before merge.'
+    })
+    const threadReactionButton = reviewThreadCard.getByRole('button', { name: 'Add reaction' })
+    await threadReactionButton.evaluate((element) => (element as HTMLElement).click())
+    await orcaPage
+      .getByRole('button', { name: 'Add rocket reaction' })
+      .evaluate((element) => (element as HTMLElement).click())
+    await expect(
+      reviewThreadCard.getByRole('button', { name: '1 rocket reaction' })
+    ).toHaveAttribute('aria-pressed', 'true')
+  })
+
   test('queues an open thread for the agent from the visible row action and menu fallback', async ({
     orcaPage
   }) => {