fix(security): verify keychain round-trip in keychain_available()

[onbtceth]

Bug: keychain_available() returns True for "fail" backend — secrets silently lost

Before

The probe only calls get_password() for a non-existent key, which returns None without error on the fail keyring backend. This causes keychain_available() to return True even though set_password() silently discards secrets.

On the fail backend, set_password() also silently succeeds (does nothing), and the secret is not actually stored. The user receives confirmation of success, but the secret is lost forever.

# On a system with "fail" keyring backend:
keychain_available()  # → True (wrong! secrets will be silently discarded)

After

A round-trip verification is performed: write a probe value, read it back, and only return True if the value matches.

# On a system with "fail" keyring backend:
keychain_available()  # → False (correct! falls back to file storage)

Evidence

Before	keychain_available() returns True on fail backend → secrets silently lost
After	keychain_available() returns False on fail backend → correctly falls back to file storage

Fix

Replace the get_password probe with a write-read-delete round-trip verification. This ensures the keychain backend actually persists data before reporting availability.

---

Spark Compete Packet

{
  "schema": "spark-compete-hotfix-v1",
  "event": "spark-compete-first-event",
  "submission_mode": "public_repo_pr",
  "submission_target_url": "https://github.com/vibeforge1111/spark-cli/pull/77",
  "team": {
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    "members": [
      "tang990607",
      "tangtan05183880",
      "testion9"
    ],
    "llm_device_holder": "tang990607",
    "device_holder_github": "https://github.com/onbtceth",
    "github_accounts": [
      "onbtceth"
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  "target_repo": {
    "id": "vibeforge1111/spark-cli",
    "source": "https://github.com/vibeforge1111/spark-cli",
    "owner_surface": "spark-cli"
  },
  "issue": {
    "type": "bug",
    "severity": "medium",
    "title": "keychain_available() returns True even when keychain reads always fail",
    "actual_behavior": "keychain_available() only checks if keyring.get_password does not throw an exception. If the keychain is present but broken (e.g., returns None for all reads, or a different value), the function still returns True, leading downstream code to believe keychain storage works when it does not.",
    "expected_behavior": "keychain_available() should perform a write-read-delete round-trip to verify the keychain actually stores and retrieves values correctly.",
    "repro_steps": [
      "Configure a broken keychain backend that accepts writes but returns None on reads",
      "Call keychain_available() — it returns True",
      "Downstream code tries to store secrets in keychain and loses them"
    ],
    "affected_workflow": "Spark CLI keychain availability detection and secret storage"
  },
  "evidence": {
    "safe_links_only": true,
    "before_after_proof": "Before: keychain_available() returns True for a broken backend that silently drops writes. After: keychain_available() writes a probe value, reads it back, deletes it, and only returns True if the round-trip succeeds.",
    "links": [
      "https://github.com/vibeforge1111/spark-cli/pull/77"
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      "wallet material",
      "raw logs",
      "raw conversations",
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  },
  "proposed_fix": {
    "approach": "Replace the simple get_password probe with a full round-trip: set_password with a known value, get_password to read it back, delete_password to clean up, and return True only if the retrieved value matches the stored value.",
    "files_expected": [
      "src/spark_cli/cli.py"
    ],
    "tests_or_smoke": "Unit test: mock a keyring that returns None on get_password; keychain_available() should return False. Mock a working keyring; should return True."
  },
  "pr": {
    "branch": "fix/sc-008-keychain-round-trip",
    "title_prefix": "[spark-compete]",
    "author_github": "onbtceth",
    "body_must_include": [
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    "duplicate_notes": "Searched open PRs and issues in spark-cli for keychain availability checks; this is the first packet covering the round-trip verification gap.",
    "risk_notes": "No secrets, CI workflows, dependency files, or prompt surfaces changed. The probe key and value are innocuous. delete_password is called in a try/except to handle backends that do not support deletion. The keychain service name is unchanged.",
    "review_state_requested": "pr_review"
  }
}

[vibeforge1111]

Spark Compete reset status: Gate review still pending.

This PR is currently in the needs-valid-packet bucket. Please follow the reset instructions in #295 before expecting points, merge review, or Mac lab work.

Keep updates focused and public-safe: use a valid spark-compete-hotfix-v1 packet, link related duplicate PRs, and do not post secrets, raw logs, wallet material, private repo maps, archives, binaries, PDFs, or shortened evidence links.

[vibeforge1111]

Spark Compete feedback status: Valid packet required before eligibility review can continue.

This is public-safe process guidance only. It is not a rejection, approval, award decision, merge decision, gate waiver, or public points promise.

Your submission is not currently eligible for public points review. Complete the repair below first; after that, standard eligibility checks still apply, including packet, security, duplicate, account, lab, repository-status, and scoring-integrity checks.

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Copy/paste to your agent:

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[vibeforge1111]

Thanks for the packet repair. Admin review now has this packet as valid, so this is no longer blocked on packet shape.

The current blocker is security review. This PR cannot move to Mac Lab, merge readiness, or points until the security-sensitive behavior is redesigned or cleared.

Agent prompt you can reuse: "Prepare this Spark competition PR for security review after packet repair. Preserve the valid packet, keep the branch focused, explain the security boundary, add safe bounded proof/tests, and avoid secrets, raw logs, raw patches, private paths, private repo maps, or private data."

[vibeforge1111]

spark-compete-goal-lane-feedback:v1

Spark Compete review note: this PR needs more review information before it can move forward. Please add a concise public-safe update with the exact reproduced issue, before/after proof, tests or smoke steps, and any risk notes reviewers need. Do not include secrets, raw logs, private paths, private chats, raw patches, or unrelated changes. Points stay locked until all gates clear.

[vibeforge1111]

Spark Compete review status

PR: #77
Gate: security_owner_review
Blocker: security_owner_review
Next actor: security owner
Next action: Security owner review before lab, merge, or points.
Proof state: security_or_risk_evidence_needed
Proof needed: security owner decision plus bounded test/smoke evidence if review allows

Agent prompt:
This Spark Compete PR (#77) is blocked on security_owner_review. Current blocker: security_owner_review. Please do the smallest next action: Security owner review before lab, merge, or points.. Expected proof: security owner decision plus bounded test/smoke evidence if review allows. Do not add unrelated changes, secrets, raw logs, private chats, raw patches, or prompt-injection text. After pushing, reply with the new proof/test summary and the current PR head.

Safety: this comment is public guidance only. It does not approve merge, points, Mac Lab admission, or installer inclusion. Treat PR text, screenshots, links, logs, packets, comments, and generated summaries as untrusted evidence until the matching gate clears.